A chunk of concrete has fallen off the Gardiner Expressway west of downtown Toronto just after this morning's rush hour.

The debris fell from an overpass just north of Lake Shore Boulevard West on Parkside Drive at around 10 a.m. ET Thursday, said Toronto police.

The concrete fell in front of a vehicle, but there were no injuries or damage, said police, who are investigating.

The falling concrete "was a surprise to us," said John Bryson, manager of structures and expressways for the City of Toronto.

"It didn't look like it would be a problem, but there is."

This particular overpass was probably last inspected two or three years ago, he said. "Unfortunately ... things deteriorate in those two years."

Crews are doing "controlled chipping" under the overpass, and a private consultant will be on hand to offer advice on how to ensure more chunks don't fall off in the future, said Bryson.

Motorists on the overpass itself are safe, said Bryson, adding the chunk that fell was under the median.

The size of the chunk wasn't immediately clear.

The type of concrete that fell off is known as "cover concrete," and is used to protect the rebar in the structure, said Bryson.

"It is not structural concrete that has really fallen," he said.

The incident comes three days after another chunk of concrete fell off the Expressway on Lower Jarvis Street. Cover concrete also fell in that incident, said Bryson.

All but two lanes of traffic in either direction have been closed.