A large sinkhole closed down part of the Canadian capital on Wednesday and forced the evacuation of businesses a few blocks from the national parliament, three weeks before Ottawa is due to host a summit of the leaders of Canada, Mexico and the United States.

The sinkhole formed on a normally busy downtown street in an area that has been under construction for Ottawa's new light-rail transit (LRT) system. City officials said the cause of the sinkhole was not yet known but earlier gas and water leaks have been contained.

"It's premature at this point to make the connection to LRT, although that could very well be the possibility," Mayor Jim Watson told a news conference.

Officials said there were no reports of injuries or missing people. The Canadian Broadcasting Corporation showed footage of a van parked on the side of the road falling into the sinkhole.

Nearby buildings that were evacuated remained closed, including the Rideau Centre shopping mall, which is owned by Cadillac Fairview, a unit of the Ontario Teachers' Pension Plan.

Buses in the area were being rerouted, and officials told Ottawans to expect travel delays on Wednesday and Thursday morning. It was the second sinkhole in downtown Ottawa in as many years.

"If you look back in the last year, there was probably a major sinkhole in every city, at least once a week somewhere in North America or around the world that's on the nightly news, and we're one more," Watson said.

The sinkhole comes ahead of the June 29 "Three Amigos" summit with Mexican President Enrique Pena Nieto, U.S. President Barack Obama and Canadian Prime Minister Justin Trudeau.