TORONTO -- A man is in life-threatening condition after being encased in hot tar that solidified during an industrial accident in Toronto on Monday morning.

Rescuers worked for more than an hour to free the man after the incident, which occurred shortly after 7:30 a.m., according to police.

Const. Clint Stibbe said the truck that was carrying a vat of hot, liquid tar, came to a sudden stop in the city's east end after the driver noticed a boom attached to the vehicle fell to the road.

There were three men in the back, Stibbe said, when the abrupt stop caused the tar, which was kept around 200 Celsius, to spill onto one of the men, trapping him inside.

"When (the tar) came out of the reservoir it went all around and when tar is exposed to the air, it hardened very quickly," Toronto Fire Services platoon chief Dave Denysek told reporters at the scene.

He said firefighters had to slice away part of the truck before slowly cutting hardened tar in small pieces away from the man's body.

Police said the 46-year-old, who they'd earlier said was 37, was breathing and conscious throughout the ordeal.

The man wasn't wearing protective clothing at the time, Stibbe said, but credited his clothing for partial protection.

"The victim suffered serious burns to his head and arms," and is in the burn unit of a local trauma centre, said Evert Steenge of Toronto Paramedic Services.

Stibbe said the man is listed in critical condition, while the other two men in the back of the truck weren't injured.

The Ministry of Labour said it had assigned staff, including an engineer, to investigate.

A ministry spokeswoman said it investigated 873 critical injuries on worksites in the province last year and 219 critical injuries in the first quarter of 2016.