A Winnipeg police officer was sent to hospital after she was assaulted while leaving the downtown Winnipeg Police Service headquarters early Tuesday morning, the WPS says.

Around 3 a.m. Tuesday, the officer was leaving the building after her shift when she saw a man interfering with a delivery person who was trying to get into the lobby.

The off-duty officer escorted the man outside the building, accompanied by two on-duty police cadets. WPS spokesperson Const. Rob Carver told reporters Tuesday that this is fairly standard procedure.

"If you see any officer, off-duty or not, doing something with an individual … you'll step up and just make sure everything is OK," Carver said.

"In this case, it wasn't."

The man suddenly turned around and attacked the off-duty officer, which led to a struggle, police say.

The officer was seriously injured and sent to hospital in stable condition.

The two cadets, a uniformed officer and an off-duty officer were able to get the man under control and arrest him.

A 35-year-old man was charged with assaulting a police officer and is still in custody.

Carver said police are unaware of any weapon being used by the 35-year-old.

"Our officers are threatened and assaulted on a regular basis. It's just not noteworthy," Carver said about why these types of incidents are not always publicized.

"Sometimes the assaults are as simple as somebody trying to throw a punch or a kick, or grabbing the officer."

In most cases, officers are unharmed, Carver said, but added that sometimes police officers get hurt and have to go to hospital.

"I think this one was unique because the officer was off-duty, leaving work," he said, adding that the fact the officer had finished her shift meant her approach to the situation had to be different than if she was on the clock.

The officer would not have been wearing body armour or been with a partner, nor would she have had a radio to call for help or access to weapons, Carver explained.

"In this case, you can be as vigilant and have your guard up as much as you can. It's just a different situation."

The off-duty officer was still in hospital when Carver spoke with reporters Tuesday morning.