A Royal Canadian Mounted Police officer standsguard on Metcalfe Street following shootings in downtown Ottawa October 22, 2014. [Photo / Agencies]

As the drama in Ottawa unfolded, police in dark bulletproof vests and carrying automatic rifles flooded the streets near parliament, clearing several blocks of downtown Ottawa.

Some took cover behind vehicles and shouted to people to clear the area, saying: "We do not have the suspect in custody. You are in danger here."

When the shooting started, most members of parliament were in the two caucus rooms past which the gunman ran. Members were told to lock or barricade themselves in their rooms or offices, and stay away from the windows.

A tweeted picture sent from the room where the opposition New Democrats were holding a weekly caucus showed a pile of chairs jammed up against the main door to prevent anyone from entering.

In Washington, a White House official said U.S. President Barack Obama had been briefed on the situation. He said the United States had offered assistance to Canada.

Canadian and U.S. stock markets declined after the shootings in Ottawa. The Toronto Stock Exchange's TSX index dropped 1.6 percent, while the S&P 500 gave back 0.7 percent.

Mass shootings are relatively rare in Canada, which has stricter gun laws than the United States, and the regulations at one point included a national registry of rifles and shotguns. Legislation was passed in 2012 to scrap the registry.

Ottawa also has a low murder rate. There were nine homicides in 2013 and seven in 2012, in a city of 885,000 people. Compared with Capitol Hill in Washington, security on Parliament Hill is also fairly low key. Anybody could walk right up to the front door of parliament's Centre Block with arms and explosives without being challenged before entering the front door, where a few guards check accreditation.

Centre Block is the main building on Parliament Hill, a sprawling complex of buildings and open space in downtown Ottawa. It contains the House of Commons and Senate chambers as well as the offices of some members of parliament, senators, and senior administration for both legislative houses.

A construction worker who was on the scene in Ottawa when the shooting began told Reuters he heard a gunshot, and then saw a man with a scarf over his face running towards parliament.

"He was wearing blue pants and a black jacket and he had a double barrelled shotgun and he ran up the side of this building here and hijacked a car at gunpoint," construction worker Scott Walsh told Reuters.

The driver got out safely, then the man drove the car to the Centre Block, where construction work is under way, Walsh said.

The Canadian military closed its bases across the country to the public following the events in Ottawa, CBC TV said.

The attacks in Ottawa and Quebec took place as the Canadian government prepared to boost the powers of its spy agency, the Canadian Security Intelligence Service. Public Safety Minister Stephen Blaney said last Thursday the new legislation would let the agency track and investigate potential terrorists when they travel abroad and ultimately prosecute them.

Related: Attacks on Canadian government buildings or politicians