Stony Mountain Institution, a medium-security federal prison north of Winnipeg, is in lockdown after a fight erupted between inmates suspected of being members of two rival street gangs on Monday afternoon.

The Union of Canadian Correctional Officers confirmed to CBC News that the incident happened at about 2 p.m. CT, with two separate fights breaking out in a hallway and in a living area.

Seven inmates have been taken to hospital, with five sustaining stab wounds and two suffering blunt-force trauma, said union spokesperson James Bloomfield.

Staff used pepper spray to get the situation under control within minutes, Bloomfield said.

"What the job is now is to take those weapons ... analyze them to see what type of materials they used to make them and then go back and try to find the missing pieces," he said.

There is no word on the conditions of the injured inmates.

Bloomfield said given the fights happened in separate areas, the union believes the attacks might have been planned. He said the drug trade may have fuelled the incident.

RCMP are now investigating the incident and the prison will remain in lockdown until further notice.

In a statement issued late Monday, the Correctional Service of Canada said it will "continue to review the circumstances surrounding this incident and take the appropriate measures."