Up to 13,000 Toronto residents are returning home after they were forced to flee a massive fire at a propane facility. A Toronto firefighter died near the scene of the blaze, and an employee at the plant is missing.

Bob Leek, a 25-year veteran firefighter, was surveying an area close to the fire at Sunrise Propane Industrial Gases when he died.

"Every effort was made to resuscitate him. However we do regret to inform everyone that we did lose one of our members today," Division Chief David Sheen told reporters late Sunday afternoon.

Leek appears to have died from natural causes, but an autopsy is expected.

"It was not a traumatic injury; he wasn't impacted by anything. It was just in the course of him performing some operations that he went down," said Sheen, who personally knew Leek, a district chief of emergency planning.

"It's hard," he added, visibly shaken by the death. "I'm sure that all of our guys are having a rough time with it."

Toronto Mayor David Miller had earlier said his "thoughts and prayers" were with the firefighter's family.

Dan Ronen, a spokesperson for Sunrise Propane Industrial Gases, said he had no idea why fireballs erupted from the plant early Sunday morning, triggering the fire.

"At present, we do not know anything about how the explosions occurred and we are waiting to learn about its cause," he said.

Ronen also told reporters that one of the plant's employees, Parminder Saini, is still missing.

He said he was praying that Saini was still alive and, if so, pleaded for the worker to contact authorities.

Thousands of people living within 1.6 kilometres of the fire had to flee their homes early Sunday, but by evening they were told it was safe to return.

There were minor injuries associated with the blast and police are still trying to determine the status of one missing person, an employee of the business -- Sunrise Propane Industrial Gases.

There were workers at the facility, which operates 24 hours per day. Cabbies driving propane-powered vehicles often use it to fill up.

However, the situation at the propane facility itself is now under control.

Sections of the 401 Highway, one of the country's busiest, are slowly being reopened between the 400 Highway, a major artery leading north out of Toronto, and the Don Valley Parkway.

Ontario Provincial Police spokesperson Sgt. Cam Wooley said it may have been the first time in Toronto that such a large section of the 401 had been closed both ways.

"I've been with the OPP for 30 years and this is the first time I've ever seen the entire 401 through Toronto closed. It's a 16-kilometre stretch," he said.

The sounds of multiple booming blasts woke up people living in North York around Keele Street and Wilson Avenue between 3:30 a.m. and 4 a.m. Fire officials determined that the explosion originated from the Sunrise facility on Murray Road.

The blast sparked a six-alarm blaze, with about 200 firefighters and 35 pieces of equipment on scene to fight the fire.

When they arrived on the scene, four propane tanks were engulfed in flames. Firefighters tried to cool the rail tankers to keep them from exploding. The rail tankers -- which were venting -- can hold up to 220,000 litres of propane, but it wasn't known if they were full, according to Division Commander Bob O'Hallarn of Toronto Fire.

"These tanks are well-designed and generally are quite safe," he said. "We'll have to investigate to see what happened."

Giant fireballs

Several people reported minor injuries as the blast blew out windows and caused major damage to several homes. Police said one person was unaccounted for, but investigators gave no further details.

He appears to be an employee at the propane facility.

The blast lit up the area with giant orange fireballs, sent smoke billowing into the sky and could reportedly be heard dozens of kilometres away.

"It was just a tremendous explosion and blew all the windows out of the house, just blew the house up, and I just managed to get out of there in time,'' said area resident Robert Helman.

"My windows just cracked and they blew out,'' said Ricardo Oliveria, 24.

"My whole room lights up orange and I look out. I live on the top floor so I had a perfect view. And I just seen a huge ball of flame hundreds of metres in the sky, big black pillars of smoke. We got freaked out. My family woke up. They thought it was a plane that went down."

O'Hallarn said his firefighters found some vehicles on fire in the area and damage to houses across the street when they arrived at the scene.

"So far we have not found anyone injured (in the houses)," he said.

Evacuees

Fire officials said residents living in a 1.6-kilometre radius around the plant had been evacuated over concerns about explosions from the tankers. Businesses in the area were forced to close.

Evacuees were taken to York University, at Keele Street and Steeles Avenue, where Salvation Army volunteers served them a hot meal. The Red Cross and the Humane Society were also at York University to help people and pets in need.

"I don't think it will be days (before the evacuees can return home), I think it will be hours but if we run into problems that we can't foresee, then it might take longer," O'Hallarn said.

Despite the risk, officials said at least two people refused to leave their homes.

Elaine Smyer, with the city's emergency planning department, was at York University overseeing the evacuees. She told reporters at the scene that crisis councillors were made available to residents who were traumatized by the early morning blast.

With files from The Canadian Press