A giant sinkhole opened up next to a major shopping mall in downtown Ottawa on Wednesday, causing a gas leak, collapsing a street and forcing the evacuation of all nearby businesses.

The sinkhole appeared about 10:30 a.m. ET Wednesday near the corner of Rideau Street and Sussex Drive, at a light rail construction site next to the Rideau Centre, about two blocks east of the Château Laurier Hotel.

City officials say it was fortunate no one was hurt. But the formation of the sinkhole, so close to the LRT site, has led to questions about what caused a water main to break and collapse the road.

Ottawa Mayor Jim Watson said at an emergency meeting of city officials it's unclear why the sinkhole formed.

Concrete trucks work to fill in a giant sinkhole on Rideau Street in Ottawa Wednesday evening after the road collapsed in the morning. (Jeremie Bergeron/Radio-Canada) "We hope to have that answer, obviously, in the next few days," Watson said.

"We just don't know how long it's going to take … it's a significant sinkhole in the downtown core," he said.

On Wednesday evening workers were pumping water out of the giant cavity in the road and filling it with concrete to stabilize the area and protect the foundations of adjacent buildings.

City Coun. Mathieu Fleury said it will be days if not weeks before the street is repaired.

Parked van fell into hole as road collapsed

Soon after forming, the sinkhole spread across the entirety of Rideau Street, stretching from the south sidewalk to the north sidewalk. A van parked on Rideau on the north side of the sidewalk, as well as a light standard, fell into the hole as it grew.

Tom Herlihy smelled natural gas before he saw the sinkhole. 'People were running away from it, you could tell something was amiss,' he said. (CBC) Tom Herlihy was on Rideau Street near the Château Laurier when he heard and smelled natural gas.

"A high-pressure natural gas line escaping is very distinct, it's a high-pressure whistle. You could smell it in the area immediately, and people were running away from it, you could tell something was amiss," he said.

Herlihy went to an upper floor of the Château Laurier to get a better look.

"I caught the hole expanding and the car falling in and the gas just roiling the water, causing the dirt underneath the street to erode and collapse. And it's really deep," he said.

Not looking good on Rideau/Sussex. Avoid the area completely. Hope everyone is ok. <a href="https://t.co/j2uNS7J6a4">pic.twitter.com/j2uNS7J6a4</a> —@JeffyE1979 Elaine Tamblyn-Watts was in a Victoria's Secret change room at the Rideau Centre when a siren rang and a voice told people in the mall to leave the building. She said the scale of the sinkhole surprised her.

"I can't believe the size of it, it's just a clear drop, the road just completely breaks," said Tamblyn-Watts.

Ottawa police are advising residents and tourists to avoid the area. Evacuated businesses include the Shaw Centre, a CIBC bank, a Chapters store and the Rideau Centre mall.

7 buildings without power

Anthony Di Monte, the city's emergency and protective services general manager, said in addition to the water main break, a gas leak also occurred, but both water and gas have since been shut off. Hydro Ottawa said as of 5 p.m. seven buildings were still without power.

Di Monte said with emergency workers mitigating damage and stabilizing the area, they haven't yet had a chance to investigate the cause.

"We don't have the basic information to formulate a plan yet for the next few days, " said Di Monte.

In the interim, the City of Ottawa said Ottawa public health is monitoring overall water quality, building code services are working with engineers on site to determine when it will be safe to re-enter buildings and city traffic managers and OC Transpo will be monitoring traffic in the downtown core.

Happened near LRT work

A crowd gathered around the sinkhole, even though Ottawa police were advising residents and tourists to avoid the area. (CBC) The sinkhole formed near a construction site for Ottawa's light rail system, which is slated to be complete in 2018. The light rail system includes a tunnel and stations that cut underneath the downtown core.

Watson noted that the excavation work on the future Rideau Station was well below where the road collapsed.

Workers were excavating the last 50 metres of the station when the road fell in, said Steve Cripps, director of the city's rail implementation office.

The soil conditions in the area where the road collapsed were sandy and rocky, requiring extra precautions and different mining techniques, said Cripps.

The Rideau Station of Ottawa's light rail line will have entrances at the Williams Street pedestrian mall and in the northwest corner of the Rideau Centre. The yellow line depicts the platform. (City of Ottawa) "This is an area where they've done all the reasonable things," said Cripps.

He said it wasn't clear whether that work was connected to the collapse. The workers left the tunnel when the collapse happened and are all accounted for, he said.

Work on the light rail transit system in the area will be suspended until the cause of the sinkhole can be determined and any necessary precautions have been taken.

A construction update from last week said station excavation at the west portal of the future station neared completion and crews were waterproofing the station and elevator pits and installing grade beams as part of the station foundation work.

Before the sinkhole formed, the road was only open to buses and taxis.