One suspect dead in Canada Parliament attack, hunt continues for possibly others.

Shots that rang out in the Canadian capital Wednesday left a soldier and a gunman dead, a city on lockdown, and a series of questions about security threats facing the nation.

Parliament member Kyle Seeback called it a "horrific day."

And it may not be over yet.

Authorities haven't ruled out the possibility that an additional shooter could be on the loose. And Ottawa Police Constable Chuck Benoit told CNN that there was more than one person involved in the shootings.

"We have to apprehend and arrest the people that are involved in this morning's incident," he said, "and at this time we don't have these people."

There were two shooting incidents in the city of Ottawa, where this kind of violence is extremely rare: one at the Canada War Memorial, which is near the Parliament building, and another round of shooting inside Parliament.

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Gunshots at Canada's Parliament

Shooting at Ottawa War Memorial

Map: Shooting near Parliament

"I was locking my bike up, and I heard four shots," said Peter Henderson, a journalist who was at the memorial at the time of the shooting. "I saw one of the soldiers laying on the ground."

The soldier appeared to have been shot in the back, Henderson said. Other soldiers who were nearby doing drills at the time ran to help, he said.

"This is a dynamic and unfolding situation. I understand that people have many questions and we are committed to providing some answers as soon as we are able," Assistant Commissioner Gilles Michaud, commanding officer of the Royal Canadian Mounted Police National Division, told reporters Wednesday.

Hours after gunshots thundered through the halls of Parliament, forcing people to barricade themselves in offices, police were still scouring the area and securing the scene.

In Twitter posts, several Canadian lawmakers hailed a top security official as a hero, crediting him with shooting the gunman inside Parliament.

"MPs and Hill staff owe their safety, even lives, to Sergeant at Arms Kevin Vickers who shot attacker just outside the MPs' caucus rooms," Craig Scott, a member of Parliament, wrote.

'I heard rapid fire'

A gunman entered the nearby building on Parliament Hill, officials said.

"I heard rapid fire -- gunshots going very loud -- and I figure maybe 20-plus shots within 10 seconds," Canadian Deputy House Leader Kevin Lamoureux told CNN. He was one level below the gunshots.

Soon, Lamoureux and others were outside the building, taken to another building nearby for safety. Others still inside were on lockdown. Some members of Parliament said on Twitter that a gunman had been killed. Police say "one male suspect" is dead.

Canadian authorities have given the name of a suspect to U.S. law enforcement and have asked for FBI assistance in tracing the person's activities, a senior U.S. law enforcement official told CNN. Only one name has been provided, and it is not clear whether the name is genuine or an alias, the official said. The official declined to provide more details, including the suspect's nationality, ethnicity and age.

A U.S. law enforcement official told CNN that a connection to terrorism hasn't been ruled out.

On Monday, a man who Canadian authorities said was "radicalized" killed a Canadian soldier with his car. The man was then shot and killed.