Two Canadian officers and two civilians have been killed in a shooting in the New Brunswick city of Fredericton. A suspect is in custody and has what police described on Twitter as serious injuries.

The shooting happened around 7:15 Friday morning in a residential area of Fredericton, which is the capital city of New Brunswick. Police have not released the names of the officers or the suspects.

For as yet unrevealed reasons, two Fredericton Municipal Police officers were responding to an apartment building. One witness told CBC that a gunman in the basement of one of the apartments opened fire on the courtyard, hitting the officers and residents of the complex.

Police have not said what type of weapon was used in the attack. One witness described it as a long gun. Another said it sounded like a shotgun.

Witnesses say they heard up to two dozen shots. It's likely that some of that fire was directed at the gunman by responding officers or the two officers who were killed since the suspect was seriously wounded.

Fredericton officers and Royal Canadian Mounted Police are at the scene. Fredericton police have notified the public through Twitter that there is no longer a threat to public safety in the area, but the scene is closed.

Local authorities have scheduled a press conference for 3 p.m. Eastern time.