LAVAL, Quebec (AP) -- An overpass near Montreal collapsed Saturday, crushing two cars whose occupants were feared dead, authorities said. At least five people were injured.

Drivers on Highway 19 slammed on their brakes and watched in horror as the overpass slowly collapsed, sending cars plunging and crushing at least two vehicles.

Quebec provincial police did not confirm any deaths but spokeswoman Chantal Mackels said police believed it was unlikely that anyone in the two crushed cars survived. (Watch rescue workers at the scene -- 2:57 Video)

"We watched the overpass slowly come down and two cars fell from it," witness Golda Simon told TVA network.

Manon Joly had just dropped her daughter off at dance school and was in her car about to drive onto Highway 19.

"I slowed down and then all of a sudden everything collapsed like a house of cards," she said. "There were three or four cars that plunged into the hole right in front of me."

Ambulances transported five people. Three were in critical condition including two suffering from head injuries.

Emergency workers had not yet reached people trapped under the wreckage, said Andre Champagne of ambulance service Urgence-Sante. The workers were trying to secure the site before attending to those trapped, he told The Associated Press.

"We know minutes are precious," Champagne said. "It takes a long time. These are heavy structures that have to be moved."

Mackels said three lanes of the overpass plus a pedestrian sidewalk collapsed onto Highway 19. She said four vehicles -- a motorcycle, two cars and a minivan -- were on the overpass at the time

The incident occurred before 1 p.m. One witness told TVA he noticed that the road sunk an inch or two when he traveled over the overpass minutes earlier and he called emergency dispatchers.

The collapse of the overpass woke up Jean-Nicolas Turcotte, who lives near the overpass.

"I was sleeping when the large crash woke me up. At first I thought it was an earthquake or an accident. I looked out the window and heard people screaming," Turcotte said. "And I saw large puffs of smoke rising."

Claude Canton was painting his house just off the highway when he heard a loud bang. He said he saw two cars that were stuck under rubble and one started to catch fire before police put it out with extinguishers.

Aerial helicopter shots showed two passenger cars and a van on their backs or on their sides over the wreckage of the collapsed overpass, blocking traffic for miles. Authorities closed the bridge connecting Laval with the island on Montreal.

The incident was similar to the 2000 collapse of an overpass, also in Laval north of Montreal, which killed one and injured two.