Emergency crews continued frantic efforts to restore power and cool spent fuel pools at a quake-damaged nuclear plant Friday as the Japanese safety agency raised its rating of the problems at the Fukushima Daiichi power complex.

Last Friday's 9.0 quake and the tsunami in Japan's northeast set off the nuclear problems by knocking out power to cooling systems at the nuclear complex. Since then, four of the plant's six reactor units have experienced fires, explosions or partial meltdowns.

Japan's nuclear safety agency bumped the alert level at parts of the Fukushima Daiichi complex from Level 4 to 5 on a seven-level international scale on Friday. Each level of the scale represents a 10-time increase in severity.

The International Nuclear Event Scale defines a Level 4 accident as having local consequences and a Level 5 accident as having wider consequences.

"Japanese authorities have assessed that the core damage at the Fukushima Daiichi 2 and 3 reactor units caused by loss of all cooling function has been rated as 5 on the INES scale," the International Atomic Energy Agency said Friday.

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Fire trucks converge in preparation to spray water at the Fukushima Daiichi nuclear plant on Friday. ((Kyodo News/Associated Press))

The Level 5 rating would seem to put it at the same level as the Three Mile Island plant accident in 1979 in Pennsylvania, where equipment and human failures led to the loss of coolant for a reactor core, causing a partial meltdown. Cooling was restored, however, and despite widespread public fears, little radiation escaped from the Three Mile Island site.

The Fukushima Daiichi accident, with explosions, fires and lethal radiation levels around the reactors, appears far more serious.

The 1986 Chornobyl, Ukraine, disaster is the only nuclear accident that was assessed at Level 7.

The IAEA said authorities assessed the loss of cooling and water supply functions at the spent fuel pool at reactor 4 as a Level 3, while the loss of cooling functions at Units 1, 2 and 4 were also rated as 3.

The rating change came as Japanese crews spent a second day spraying seawater on one of the plant's reactor units.

Japanese self-defence force members started spraying Unit 3 from the ground and the air on Thursday, and ground crews returned to the scene Friday to douse the fuel pools again, broadcaster NHK reported.

Special fire engines, including one lent by the U.S. military but operated by Japanese workers, were in use, NHK said.

What is the International Nuclear Event Scale?

The International Atomic Energy Agency introduced the International Nuclear and Radiological Event Scale in 1990 as a worldwide tool for communicating to the public in a consistent way the safety significance of nuclear and radiological events.

Events are classified on the scale at seven levels: 1–3 are called "incidents" and 4–7 "accidents."

The scale is designed so the severity of an event is about 10 times greater for each increase in level on the scale.

While crews worked to cool the reactors, the plant's operator, Tokyo Electric Power Co., is trying to restore power to at least part of the damaged plant.

Nuclear agency spokesman Hidehiko Nishiyama said Tokyo Electric aims to restore electricity to the plant's No. 1 and 2 reactors on Saturday and the No. 3 and 4 reactors by Sunday. Electrical equipment at the plant has been damaged by the tsunami, however, which makes it less certain when cooling functions can be restored.

Nishiyama rejected suggestions that the plant should be buried in sand and concrete, as was done at Chornobyl, to prevent a massive radioactive release. Experts say the reactors must be cooled, because simply burying them could lead to a total meltdown that would be even more hazardous.

''What we need to do now is to cool the reactors' cores, make sure that electricity will be restored and re-establish the cooling functions'' at the plant, he said.

Jeremy Whitlock, a reactor physicist with Atomic Energy of Canada Ltd., said it appears that progress is being made, despite the increased alert level.

"Currently, we're not out of the woods," he said. "But it looks to be that it's in a stabilizing condition.

"What's happening in the plant is very dire, and very grave, and lots of good people are working around the clock in very harsh conditions, but it's always about what you are measuring offsite," Whitlock said.

He said that  "we haven't had significant radiation releases offsite for the public, and that's always the final concern in this case."

In Geneva, the World Health Organization said Tokyo's radiation levels are increasing but are still not a health risk, and the group sees no reason to ban travel to Japan because of its nuclear crisis.

WHO spokesman Gregory Hartl said Friday the organization "is not advising travel restrictions to Japan" outside the 30-kilometre exclusion zone around the Fukushima Daiichi complex.

Canada is deploying nine more radiation monitors on B.C.'s coast, in addition to six units already in place, said Dr. Paul Gully, senior medical adviser for the Public Health Agency of Canada. This is a precautionary measure, and no heightened radiation has been found in air flow from Japan that has reached Canada, he said.

The government has no plans to screen passengers from Japan for radiation, saying there is no health risk to anyone who has not been within a 30-kilometre radius of the Fukushima Daiichi power plant.

'Racing against the clock'

Meanwhile, Yukia Amano, head of the International Atomic Energy Agency, said he believes Japanese authorities are "racing against the clock," and called for more support.

"This is not something that just Japan should deal with, and people of the entire world should co-operate with Japan and the people in the disaster areas," Amano said.

Edano said Tokyo is asking the U.S. government for help and that the two are discussing the specifics.

"We are co-ordinating with the U.S. government as to what the U.S. can provide and what people really need," Edano said.

Japan's national police agency said Saturday that 7,197 people are dead and 10,905 are missing after last week's earthquake and tsunami. Some of the missing may have been away from home at the time of the quake, but many others are believed to have been swept out to sea by the tsunami, and few of those bodies are likely to be found.

Rescues have been few, and a report Saturday that a young man had been pulled from a crushed house in Kesennuma city proved to be incorrect.

He apparently had been in an evacuation centre and returned to his home, where he lay down on a blanket.

Police said more than 452,000 people made homeless by the twin disasters were staying in schools and other shelters, as supplies of fuel, medicine and other necessities ran short. Both victims and aid workers appealed for more help, as the chances of finding more survivors dwindled.

About 343,000 Japanese households still do not have electricity, and about one million have no running water.

Leaving Sendai

On Friday, just after 10 p.m. local time, a bus arrived at the Canadian Embassy in Tokyo after a 10-hour drive from the hard-hit city of Sendai, CBC's Amber Hildebrandt said.

Twenty-one people, including 16 Canadians, were on the half-full bus chartered by the Canadian government.

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Municipal office employees observe a minute of silence in Tono, northern Japan, on Friday, to mark the one-week anniversary of the deadly earthquake that triggered a tsunami and nuclear crisis in Japan. ((Yuriko Nakao/Reuters))

Christian Skott, 29 an English teacher from Vancouver who has been living in Sendai, was one of the passengers who decided to get out of the devastated coastal community for now. His wife, two-month-old daughter and sister-in-law were with him.

Skott, 29, said he was walking through a parking lot with his wife and child when the quake struck last Friday.

"For the first couple of days, I was in the dark and I didn't know what happened."

He said he realized how lucky he was when he saw footage of the widespread devastation on television.

The Department of Foreign Affairs said there are roughly 11,000 Canadian citizens in Japan. Foreign Affairs officials are working closely with their counterparts to identify Canadians in need of assistance, the department said.

Asked about how he feels about the Canadian Embassy's reaction to the disaster, Skott said: "They dropped the ball on this one big time."

Skott said some Canadians in quake-affected communities didn't even know about the bus to Tokyo. He said he called up friends to tell them about the bus. "They said, 'What bus? what are you talking about?'"

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With files from CBC's Amber Hildebrandt, Kyodo News and The Associated Press