It's likely to take several weeks to re-open a major thoroughfare in Ottawa that was cut off Wednesday when a cavernous sinkhole opened up underground and swallowed three lanes of pavement, the sidewalk and a parked minivan.

Determining the specific cause of the road collapse will take even longer, Ottawa Mayor Jim Watson said Thursday.

Initially, Watson said city staff estimated it would be two or three weeks before the road is fully repaired. He later revised the prediction to between one and two weeks.

Overnight, Watson said crews poured 2,700 cubic metres of concrete into the gaping hole — the equivalent of about 300 truckloads.

Many businesses began reopening just one day after the collapse as crews restored electricity to the area Thursday morning. Natural gas service was expected to be available again by the end of the day.

However, a precautionary boil water advisory was also issued for area businesses.

No one was injured as the sinkhole opened, despite the fact the road was being used as a bus and taxi transitway while crews beneath were digging a tunnel for a new light rail transit line in the area.

Approximately 5,000 people work in the vicinity and roughly 20,000 people on average make their way daily through the busy Rideau Centre shopping centre that was evacuated when the road that runs alongside the mall collapsed.

The cause of the sinkhole has not been determined, said Watson.

"I want the public to be reassured that we are putting in all of our resources to determine the cause of the situation," said the mayor.

"We are currently focused on the rehabilitation and reoccupancy of the affected buildings, but we are committed to providing the public with regular and timely updates as information develops."

Pinpointing the cause, he said, could take "a couple of months."

The sinkhole formed at mid morning Wednesday a few hundred metres from Parliament Hill, near the corner of Rideau St. and Sussex Drive, just two blocks east of the Chateau Laurier hotel.

The resulting hole stretched across the entire width of the street, measuring about 40 metres long and 28 metres wide with an average depth of about five metres, said Steve Cripps, manager of the city's rail implementation office.

The ground in the area consisted of sand, silt and fractured rock that construction crews knew was unstable.

But officials said Wednesday they were unable to say whether the soil conditions were a contributing factor.

The road collapse came three weeks before a major North American leaders' summit that's set to take place June 29, which was already expected to add to the city's traffic headaches.

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