MONTREAL, Aug 2 (Reuters) - Montreal banned trucks from using an overpass on a major city thoroughfare on Thursday because of concerns about the bridge's structural safety.

Montreal Mayor Gerald Tremblay said the ban on truck traffic over the Boulevard Henri-Bourassa overpass at Boulevard Pie-IX in the city's northeast end will remain in effect until engineers complete a detailed inspection of the structure. Traffic will also be reduced to four lanes from six lanes.

The weight restrictions, which do not include buses or cars, stem from a public inquiry into the collapse of the Concorde overpass in the Montreal suburb of Laval last September in which five people were crushed to death, including a pregnant woman. Six people were injured.

They also come a day after the collapse of a U.S. highway bridge into the Mississippi River at Minneapolis. That disaster killed several people and injured about 60, with more than 20 still missing.

A Quebec government inquiry into the Concorde incident identified 135 bridges and overpasses across the Canadian province of 7.5 million that require detailed inspections because of concerns about structural safety.

The province banned extra-heavy trucks from using the overpasses during the inspection period, which could take several weeks.

At a press conference, Mayor Tremblay referred to Quebec's aging overpass problems and Wednesday's collapse of the U.S. highway bridge.

"I admit that I am still affected by the images from the tragedy of the Concorde overpass, the tragedy yesterday on the bridge in Minneapolis, and those from a expressway under construction that collapsed recently in Los Angeles," Tremblay said.

"We have to act responsibly and ensure the safety of our citizens," he added.

Earlier this week, Montreal flagged nine overpasses that require inspection and repair and restricted truck traffic on them.

Industry officials and experts have raised questions about the design, construction, maintenance and inspection of many of the province's 332 concrete overpasses, especially those built in the 1960s and 1970s without embedded reinforcing steel.

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