Thai authorities extended a curfew in Bangkok and numerous provinces by three more nights Thursday as smoke billowed from buildings in the capital city and troops exchanged occasional gunfire with holdout protesters.

Until Sunday morning, the curfew on Bangkok and 23 provinces will be in force from 9 p.m. to 5 a.m., army spokesman Col. Sansern Kawekamnerd said.

A curfew was first imposed Wednesday night and followed an army crackdown on the anti-government encampment. Despite the curfew, sporadic clashes between troops and remaining protesters continued after dark.

Six bodies were found at a temple that had been used for shelter by hundreds of protesters, but it was unclear when those people died.

Sansern also told reporters that authorities found a cache of bombs, "war ammunition" and guns including AK-47 and M-16 automatic rifles during the crackdown.

In a televised address Wednesday, Prime Minister Abhisit Vejjajiva said he was confident that order could be restored, but he added that soldiers had permission to shoot suspected arsonists.

"Please rest assured that the government, officers and I are confident and determined that we can overcome the problems," he said.

Government security forces stormed into the Red Shirt protesters' sprawling encampment Wednesday in a pre-dawn raid, using armoured vehicles to smash through barricades made of tires and bamboo sticks.

At least seven people, including an Italian photographer, were killed in Wednesday's clashes. Dozens more were wounded in the crackdown — including Chandler Vandergrift, a Canadian freelance journalist.

A massive fire tore through Central World, one of the largest shopping centres in Southeast Asia, and the Thai Stock Exchange was also set ablaze, reports said.

Staff at a Thai television station said they moved out of their building after a group of protesters attacked the facility and threatened to burn it down. More than 25 buildings were damaged by fires Wednesday, government officials said.

Cabinet minister Satit Vongnongteay described the chaos as anticipated "aftershocks."

"There are violent-prone protesters who remain angry," Satit told a news conference.

Canadian wounded

Vandergrift is a writer, photographer and conflict-management consultant who has been documenting the tensions between protesters and the government.

"As with any Canadian that comes in harm's way, we're working closely with Thai authorities and the hospital involved and tracking the individual's condition," said Ron Hoffman, Canada's ambassador to Thailand.

He said privacy laws prevented him from providing any details on Vandergrift's health status.

The Canadian Embassy in Bangkok has been closed because of its proximity to the site of the clashes, but Hoffman said officials are still providing emergency services to Canadians in need of assistance.

Vandergrift is the second Canadian freelance reporter to be injured in the clashes. Nelson Rand, a Canadian-born reporter working with the France 24 television network, was struck by three bullets while covering anti-government protests in Bangkok last week.

Red Shirt leader surrenders

A Thai medical technician attends to a casualty on the front line of Wednesday morning's pre-dawn raid in Bangkok. (Anthony Germain/CBC)

Many Red Shirts are supporters of former prime minister Thaksin Shinawatra, who was ousted in a 2006 military coup. They believe the current government came to power illegitimately through manipulation of the courts and the backing of the country's military.

The protesters, many of them rural poor, want Vejjajiva to dissolve parliament and call a new election.

The army urged protesters to leave the site early Wednesday before it moved to end the standoff.

Several senior Red Shirt leaders surrendered to authorities after urging their supporters to leave the area and go home. They said they are formally ending the protest to prevent further bloodshed.

"Brothers and sisters, I'm sorry I cannot see you off the way I welcomed you all when you arrived here. But please be assured that our hearts will always be with you," Nattawut Saikua, a key leader, said as he was arrested.

"Please return home," he said.

Government spokesman Panitan Wattanayagorn declared the first stage of the army operation to secure the area around Lumpini Park successful, though the advance was stalled by sniper fire from Red Shirts, Associated Press journalists reported.

Previous attempts to negotiate an end to the standoff — which has destabilized a country once regarded as one of Southeast Asia's most stable democracies — have failed. A government offer earlier this month to hold November elections foundered after protest leaders made more demands.

At least 42 people have been killed, most of them civilians, over the past week in Bangkok.

With files from The Associated Press