Germany will close airspace over its northern cities early Wednesday because of high levels of ash from an Icelandic volcano, the country's meteorological service says.

Authorities said flights and landings would be halted at Bremen airport and Hamburg airport at 5 a.m. and 6 a.m. local time respectively, and that airspace over Berlin and Hanover could also be affected.

Hundreds of flights to and from Scotland and Northern Ireland were cancelled Tuesday as a cloud of ash from the volcano Grimsvotn continued to affect air travel.

Brian Flynn, head of network operations at Eurocontrol, the European air traffic agency, warned that up 500 flights would be affected, including in some Scandinavian countries.

Icelandic officials said the amount of volcanic ash being released was decreasing, and they don't expect air travel to be disrupted as much as last year, when millions were stranded after the eruption of the Eyjafjallajokull volcano.

British authorities, however, said concentrations of ash in the skies over Scotland were high. 

"All the data we are receiving confirms our forecasts, that there is high-density ash over Scotland," said Barry Grommett, spokesman for Britain's weather agency.

Irish budget airline Ryanair said the cancellations were an overreaction, saying it had sent its own airplane into Scottish airspace and found no ash in the atmosphere.

"Exactly as we predicted, we encountered absolutely no problems, Ryanair's chief executive Michael O'Leary told The Associated Press. "There's no cloud over Scotland. There's no dusting of ash on the airframe or the wings. The airspace over Scotland should never have been restricted in the first place."

Ryanair was forced by Irish authorities to cancel all 68 flights in and out of Scotland for the rest of Tuesday. Seven other airlines — most of them regional carriers — also grounded their Scottish flights.

In Norway, two daily flights between the mainland and the Arctic islands of Svalbard cancelled until further notice. Occasional flights to and from Iceland and Stavanger in western Norway have also been cancelled.

Air Greenland cancelled two daily flights between Greenland and Copenhagen after Greenland airspace partly closed. Air Iceland cancelled flights to and from three destinations in Greenland.

In Denmark, authorities said airspace was closed in the northwestern part of the country, while ash caused some delays and cancellations in Copenhagen.

Heathrow airport had not been affected, CBC reporter Nahlah Ayad said in an interview from London.

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"The good news is is that so far, the European transport officials are saying that they don't expect this to last as long as last time or to be as bad as last time partly because the concentration of the ash itself will be low compared to last time and also experts are saying that the particles in this ash cloud are heavier than last time so they're falling faster and closer to Iceland than they did last time."

This latest volcanic eruption in Iceland has so far not packed the same punch as last year's. In April 2010, another volcanic eruption grounded planes across northern Europe for five days, stranding some 10 million travellers. Thousands of flights were grounded and airlines lost millions of dollars after the Eyjafjallajokull volcano blew.

This time, there seems to be a more measured response. While flights have been cancelled in Scotland, airports remain open. And airlines are being given more leeway in deciding whether its safe for their planes to fly.

Because of what happened last year, British government officials said they are now better prepared to avoid a similar mass grounding of planes. New guidelines can determine which airline fleets are safe enough to fly through low- and medium-density ash clouds, Phillip Hammond, Britain's Transport Secretary told CBC News.

"Since then, a lot of work's been done with the engine manufacturers, with the airframe manufacturers, airlines, with other regulators around the world who have experience of volcanic ash conditions."

The result is that regulators have raised the levels of ash through which they believe aircraft can fly safely.

The Grimsvotn volcano began erupting on Saturday, sending clouds of ash high into the air. The amount of ash spewing from the volcano tapered off dramatically on Tuesday, however, said Elin Jonasdottir, a forecaster at Iceland's meteorological office. She added that because the plume has decreased in height — it's now at about 5,000 metres — the ash won't travel far and will most likely fall to the ground near its source.

The ash cloud caused U.S. President Barack Obama to cut short his visit to Ireland on Monday.

Meanwhile, Barcelona's soccer team was to travel to London on Tuesday, two days ahead of schedule, for Saturday's Champions League final against Manchester United. Barcelona is making the trip early to avoid having its Champions League travel plans disrupted for a second consecutive year by volcanic ash.

With files from The Associated Press