A single transport truck carrying a flammable, hazardous chemical has rolled over on the Queen Elizabeth Way highway west of Martindale Road in St. Catharines, prompting police to close the road and issue an evacuation order for  a 2-kilometre radius of the site.

Residents are being asked to shelter in place, while businesses are being evacuated.

The 2K radius is an expansion of an earlier 1K evacuation range.

"We're asking people to stay in their homes and shut down their windows. We believe the chemical is contained," said Const. Phil Gavin of Niagara Regional Police Service. "It is not an airborne issue but we don't want people moving around."

Police are also asking people inside vehicles in that area to stay put and are asking those outside of the radius to avoid it for the time being. 

Gavin said if any residents need to be evacuated, a police officer will come to their home to escort them. 

The QEW is closed eastbound and westbound between Highway 406 and Ontario Street in St. Catharines as a result.

The closures will be in place for several hours while the hazmat team determines how to move the truck safely.

Stephanie Sabourin, a media relations specialist with the Niagara Regional Police Service, says they are hopeful they will have the highway reopened for the morning rush, but aren't offering any guarantees.

Ontario Provincial Police Sgt. Kerry Schmidt said the truck was hauling phosphine, which is dangerous when inhaled and is flammable. It wasn't immediately clear whether the substance had leaked. The rollover involved just the one transport truck.

The truck is partially over the centre guide rail on both eastbound and the westbound lanes of the highway, Schmidt said.

Fire departments are on scene to manage the hazardous material. Police are escorting cleanup crews to the site as quickly as possible from both the east and the west, Schmidt said.

The OPP is still investigating and trying to determine what caused the crash. 

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Jessica Troup on Twitter tweeted another photo once police were on scene at the site of the crash. (Twitter)

Police released a map of the area under evacuation order.

They say the evacuation is precautionary, with no immediate risk to the public. The wind is blowing eastward, the police said. 

Schmidt said it appeared to be a mechanical issue that caused the crash. There were no injuries reported.

Schmidt said to expect heavy delays in both directions, and a small number of residents and businesses near the QEW in St. Catharines might be visited by a police officer asking them to evacuate. 

OPP shared detour instructions: 

Selena Jensen works at Cafe Amore, in a strip mall off of Martindale Road. She told CBC News that no one had come to the door yet but that the restaurant was within the evacuation zone. 

"We're being evacuated right now," she said. ""They're in the mall and they're telling everybody to go."

Jessica Troup was on her way to Niagara Falls for the evening with her boyfriend when they saw the overturned truck on the centre divide.

Troup said they were only delayed about 15 minutes. But she's concerned about hearing that there was toxic chemical in the truck.

"I am worried," she told CBC News. "I didn't smell anything. I'm waiting for the reports to say whether the containers are intact or not."