Toronto Fire says an area in Etobicoke that was evacuated on Sunday for about four hours has been reopened following a "large" ammonia leak that sent two people to hospital.

Capt. David Eckerman, spokesperson for Toronto Fire Services, said the fire department received a call about the leak at a frozen food company on Evans Avenue west of Kipling Avenue at about 8:29 a.m.

By 11:20 a.m., fire crews had shut off a main valve in a compressor room where the leak began, thereby stopping the leak at its source, and by noon, Toronto Fire declared the emergency over.

Fire crews evacuated three residences, some businesses and the TTC's Queensway yard. The area that was blocked off had a radius of about 150-metres, or 500-feet.

"We will slowly be letting people back in the area," Eckerman said Sunday. " Normal activity in the area is expected to resume."

Two people were sent to hospital, including a man in his 50s who had trouble breathing, he said. 

Ammonia leak 2

Fire crews, with the help of police, evacuated the area immediately after the leak was detected. The area, on Evans Avenue West of Kipling Avenue, has since been reopened. (CBC)

"It's a caustic material. It creates a burning sensation in the lungs," he said.

GO Transit and Canadian National had stopped train traffic on nearby rail lines due to the leak but have resumed operations. 

Eckerman said the building was vacant when the leak began. The leak spilled into a room and spread out onto a floor.

When fire crews arrived, they entered the building to assess the hazard, then left because of the fumes. Crews notified the company, which sent a plant operator and technician to the plant to repair the leak. 

Eight fire trucks and 35 firefighters in all responded to the call. 

Fire crews also notified Ontario's ministries of labour and health. 

Area 'saturated' with smell

Eckerman was unable to say how much ammonia in liquid form was spilled, but said the leak was large. 

Ammonia leak

An ammonia leak on Evans Avenue, pictured here, has sent two people to hospital from exposure and led to the evacuation of a small area in Etobicoke. (Google Street View)

"The area was saturated with the smell and the aroma of the ammonia outside of the plant itself. Anything that is of such a quantity that it could be detected from the exterior of a building, I would describe as large," he said.

Const. David Hopkinson, spokesperson for Toronto Police Service, said police helped firefighters to evacuate the area.

Evans Avenue, which was closed from Bellman to Kipling Avenues, has been reopened.

According to the Canadian Centre for Occupational Health and Safety, ammonia is toxic if inhaled and corrosive if contact is made with skin. It can irritate the nose and throat, burn the skin and damage eyes. It can harm respiratory systems.

Ammonia is a colourless gas and high concentrations can be a fire and explosion hazard.