Dr. Baird said that this is because early measures on earthquakes are often inaccurate. "It takes a bit of time to actually process the data to get an accurate measure of the magnitude," he said. Similarly, he said, early reports that the earthquake was 18 kilometres in depth may turn out to be inaccurate.
Environment Minister Jim Prentice was doing an interview with CTV at its Ottawa bureau on the 14th floor of the World Exchange Plaza in downtown Ottawa when the tremor struck.
"I was on the air and suddenly my chair was moving," he said afterwards. "Fortunately I was at the end."
The sidewalks quickly filled with workers who decided to evacuate their buildings. Within minutes of the tremor, cellphone service in Ottawa was down, possibly because callers had overloaded the system, though the exact cause was not known.
Twitter users as far away as Springfield, Mass. and Traverse City, Mich. reported feeling tremors. The quake was felt in Michigan, Vermont and parts of upstate New York.
Sara MacIntyre, a spokeswoman for the Prime Minister, said Stephen Harper was in a car on his way to the Ottawa airport at the time of the earthquake and didn't feel the tremors. Mr. Harper continued with his flight to Toronto to attend an Air India bombing memorial. Ms. MacIntyre said Langevin Block, which houses the Prime Minister's Office, was not evacuated.
"Everyone's okay. We were all not accustomed to the sensations obviously but recognized almost immediately what it was and everyone kind of grouped together," she said, noting that security guards checked in on workers.
On Parliament Hill, where the Commons has adjourned for the summer but the Senate was still in session, Senators felt the Red Chamber shake. Glass windows made a crunching noise, and ornate chandeliers swung.
"I was walking into the chamber, and there was all this crunching noise, and all of a sudden everyone started running," said Senator Marjory LeBreton.
The Senate's black-robed officers poured onto the Parliament lawn, with deputy usher of the black rod carrying the ceremonial staff.
"We're having some contentious debates, so we were wondering if it was a message from the gods," Sen. LeBreton joked.
Parliament Hill was evacuated after the earthquake and Public Works is in the process of inspecting the buildings for possible damage, said Heather Bradley, a spokeswoman for the Speaker of the House of Commons. Employees are being allowed to retrieve their personal belongings and are being asked to go home for the day, she said.
A PMO spokeswoman said the Ottawa headquarters of the National Research Council, which is responsible for monitoring earthquakes in Canada, has been evacuated and officials are taking phone calls from an emergency room.
The Bank of Canada, a few blocks from Parliament Hill, has been closed until the building has been inspected and deemed safe. Core staff will carry on operations out of the bank's second site, which is outside of the downtown core.
Jill Vardy, the Bank of Canada's deputy chief of communications, said this is standard procedure after earthquakes of a significant magnitude.
She said the bank is expected to reopen at its primary site on Thursday.
The tremors were also felt in the Ontario legislature's grand stone building at Queen's Park, prompting one government official to send an email to officials in Quebec, jokingly saying: "If you wanted to separate, why didn't you just say so."
Mike Ansell, manager of a senior citizens home in Cumberland, Ont., said the shaking was "huge" and "felt like forever, but probably just lasted a few minutes."
"Suddenly, I felt the floor moving, and I thought it was an explosion or something," he said. "I immediately thought terrorists or something."
All 65 residents were evacuated safely, he said, and there didn't seem to be any major damage on the streets around him.