A glimpse of the explosion lighting up the pre-dawn sky in northwest Toronto, between Highway 401 and Downsview Park. (Submitted by Andrew Erlich)

Toronto will review all industrial areas that could potentially pose a threat to residential neighbourhoods.

The decision comes a day after a massive explosion and fire at a propane plant in the city's northwest.

On Monday, Toronto Mayor David Miller told CBC News he wants to know if similar risks exist elsewhere in the city and whether zoning bylaws need to be changed to ensure public safety.

"Many of them [bylaws] are many years out of date," Miller said in a telephone interview from his office.

"Zoning, in this example, for example, has probably been there for 30 or 40 years and we need to determine if we can put distancing requirements in if there are other examples of facilities this close to residential neighbourhoods."

The propane depot that exploded over the weekend was regulated and authorized by a provincial agency and complied with existing zoning laws. But Miller said he has heard concerns about safety issues at the plant.

"The people told me they'd seen people smoking at the site. They'd told me that they'd seen flames there. And they told me that they'd seen driving that was irresponsible and a danger. I don't know if any of those, of course, are true or isolated incidents, but it's enough to raise a concern," he said.

Toronto's acting deputy mayor Shelley Carroll said propane experts and the Ontario Fire Marshal are reviewing past inspections of Sunrise Propane Industrial Gases in an effort to determine the cause of the early Sunday explosions.

The series of blasts that started about 3:50 a.m. resulted in the death of a veteran firefighter and forced about 10,000 residents to flee their homes as a fireball illuminated the sky above them.

Bob Leek, 55, Toronto Fire Services district chief of emergency planning, was found unresponsive at the scene and was pronounced dead at hospital, authorities said. It is unclear how Leek died and cause of death is still to be determined.

Crews continued to search on Monday for a Sunrise Propane employee who has been missing since the explosions. More than a dozen residents were also injured when their homes were damaged.

Most residents have returned home

Most of the 12,000 area residents forced to leave their homes were allowed back on Sunday evening, but a number of homes suffered heavy damage so owners have not been permitted to return.

Stuart Green, a spokesman for the mayor, said the city wants to know if similar risks exist elsewhere in the city and whether zoning bylaws need to be changed to ensure public safety.

Many residents are angry that the plant was allowed to operate so close to their neighbourhood.

Green said old municipal bylaws permitted the plant to operate in the area, and that all facilities with chemicals or gas must receive provincial approval.

As the blasts went off around her, Vicki Arciero ran from her house dressed only in her bathrobes, clutching her dog.

"For the last six months, my daughter has actually been saying to me, 'Mom, we've got to move, this is a dangerous place, what if it blows?" Arciero told CBC News.

Busy highways shut for hours

The blasts and fire also forced the closing of two of Canada's busiest highways, the 401 and the 400, for the day.

The highways were both open Monday morning.

"We got the okay to open the ramps this morning," said OPP Sgt. Cam Woolley. "Yesterday [Sunday] it was the biggest closure we've ever done in Toronto: 16 lanes of the 401 shut down for 16 kilometres."

Carroll said it is always a "huge fight" for municipalities to hang on to what industrial zones are available amid the pressure to increase population density.

"But this is a very tragic lesson in why we have to have the authority to do that," she said.

Federal Public Safety Minister Stockwell Day said pending investigations will look at the land use and determine if it was appropriate.