MONTREAL - A large chunk of concrete fell from the ceiling of the Viger Tunnel Sunday morning, closing the Ville Marie Expressway completely to traffic in both directions between De la Montagne and Panet.

The westbound segment of the highway was reopened in the mid-afternoon but the eastbound side remains closed indefinitely.

"Within a few seconds, everything fell down," construction worker Pierre Dacosta told CTV Montreal's Aphrodite Salas. "There were machines nearby that were shaking everything hard, then the whole thing fell."

The incident happened on Highway 720 eastbound about 9:20 a.m. Sunday morning near the Hotel-de-Ville overpass. No one was injured and no one was trapped inside the tunnel at the time, said police.

Workers were on site maintaining a wall in the tunnel when a cement beam fell from the eastbound Ville Marie, according to Caroline Larose, a representative of the provincial Minister of Transport. She could not specify what sort of work was underway or whether it was related to the collapse. 

The slab fell in a section of the Ville Marie between he Hotel-de-Ville overpass and just before the entrance to the tunnel. The object that fell was a cement support beam for the sun shades designed to diffuse light overhead.

Mayor Gerald Tremblay held a press conference at the site Sunday afternoon and mentioned that he would be meeting with provincial Transport Minister Sam Hamad later that evening.

He said that parking will be banned on Ontario, St-Antoine and Rene-Levesque to allow for an extra lane to be opened to deal with the extra traffic.

"With the problems on the Mercier Brige, the Champlain Bridge, the Turcot Interchange and now the Ville Marie, these problems are piling up but that is no reason to panic," said Tremblay. "That's why I am here with my team to say that we will not cut any corners when it comes to the safety of our citizens."

Larose, meanwhile, said she did not know if there was any connection between the collapse and digging at the nearby St-Laurent exit for a pedestrian tunnel to the French superhospital. Larose stressed that the structure is regularly inspected and maintained as part of the $4-billion annual highway maintenance budget. She could not, however, say when the last time inspectors had studied the roadway.

Eastbound traffic was closed indefinitely as the massive chunk, around 15 metres-long, blocked the highway.

Westbound traffic was closed as the highway on that side underwent inspection but it was reopened around 3 p.m.

Larose could not say when the highway would be reopened but confirmed that it definitely closed for the rest of Sunday.

The highway serves about 100,000 cars on weekdays but the morning traffic was quiet on this Sunday morning during the Quebec construction holiday.

As of Sunday afternoon, dozens of emergency officials and other authorities were on hand but no attempt had been undertaken to remove the massive piece of concrete from the roadway.

The fallen chunk of concrete supports a sun shade that serves the function of helping drivers' eyes adjust to the darkness while entering the tunnel. The anti-glare shade itself also came down.

One worker, who asked not to be identified, told the Canadian Press that he thought the vibrations from the repairs may have led to the collapse.

If the incident was caused by work being undertaken Sunday morning, it means the work was not properly executed, planned or supervised, according to Montreal Civil Engineer Hellen Christodoulou.

"You have to take the precautions. If the work caused the collapse, that means it was not appropriately done," she told CTV Montreal.

She adds that there is mounting evidence to suggest that there is an issue with the way the government is approaching such problems.

"We've had the Concorde Bridge, at the time it was said that 135 bridge structures had to be repaired or replaced but it was not considered urgent. But the bridge industry requires a proactive approach," said Christodoulou. "These problems show that the situation warrants big changes."

The incident is the latest in a series of infrastructure problems on the city's roads and bridges.

The emergency construction work on the Champlain Bridge and the city's biggest highway interchange has led to nightmarish traffic jams at odd hours, even in the dead of summer.

The incident on Sunday also brought back memories of the 2006 collapse of a highway overpass in nearby Laval, which killed five people and injured several more.

The Ville Marie Tunnel opened May 23, 1974 after construction started three years earlier. In total it consists of about 7.6 kilometres of underground highway.

The tunnel originally cost $120 million to build and now contains a sophisticated system that controls ventilation, lighting, cameras, and emergency exits.

The tunnel descends 36 metres below the surface, placing it below the water level at certain points. Heated cables are placed in the joints to prevent water seeping through from freezing and causing damage.

With files from Canadian Press