Canadian police mounted a massive hunt on Thursday for a 24-year-old man armed with high-powered weapons who they suspect shot dead three police officers and wounded two more in the eastern city of Moncton.
The incident was one of the worst of its kind in Canada, where fatal attacks on police are rare.
Police cordoned off a large area in the city's northwest and warned residents to stay inside their homes and lock their doors. A large armored police truck entered the area early on Thursday morning and a helicopter hovered overhead.
Schools and government offices were shut in the city of 70,000 in the East Coast province of New Brunswick.
Police told residents not to tweet the locations of officers for fear they could be helping the suspect, who they named as Justin Bourque. He has no previous criminal record.
Police said Bourque had been spotted three times in Moncton since the shootings, most recently just after dawn on Thursday, but was still at large.
"This is a very very dangerous situation as we speak ... We have not apprehended the individual," said Roger Brown, commander of the Royal Canadian Mounted Police in New Brunswick.
"This is like working through your worst nightmare," he told a televised news conference in Moncton.
Police were alerted on Wednesday afternoon by a member of the public who spotted an armed man walking down a residential street. When police arrived, the man moved into a nearby wooded area and opened fire. Three officers were killed and two more were taken to hospital, where they were undergoing surgery on Thursday.
Mass shootings are relatively rare in Canada, which has stricter gun laws than the United States, and the killings have spurred an outpouring of grief on social media.
The last mass killing of police took place in Mayerthorpe in the western province Of Alberta in 2005, when a gunman killed four officers before shooting himself. Those deaths were the most the RCMP had suffered in a single day in 100 years.
Brown said the entire RCMP was in mourning after what he called a horrendous crime. Earlier in the day he visited some relatives of the dead and injured. "They are hurting. There is actually no way to describe the level of hurt," he said.
Media in Moncton published a photograph of a man in camouflage clothing and a black headband carrying a rifle. Reuters could not immediately authenticate the picture.
A Facebook page purporting to belong to the shooter was filled with posts critical of the police and those who back gun control.
City officials said there had been no murders in Moncton in all of 2013, and none had been recorded this year until Wednesday.
Lorraine Roy, 76, lives with her husband in an apartment in the area under lockdown. She told Reuters by phone: "We heard the helicopters all night and kept our lights off all night. We are on the third floor and did not want to take any chances if someone pointed a gun this way."
She said she was shocked by the events because "Moncton is a very quiet and safe place, especially this area. The only place where there are problems is around the pubs downtown sometimes."