Firefighters and a haz-mat crew surround the Public Safety Building in downtown Winnipeg on Wednesday. (CBC)

The downtown headquarters of the Winnipeg Police Service was evacuated Friday — the second time this week.

Haz-mat crews were sent to the Public Safety Building on Princess Avenue just after 10 a.m. after staff complained of a solvent smell.

Complaints came from people on all four floors, said spokeswoman Const. Jaqueline Chaput, adding three staff members were treated on scene for minor symptoms including headaches and nausea.

A fourth staff person was sent to hospital as a precaution, but all four were feeling better by the late afternoon, she said.

Mike Sutherland, president of the Winnipeg Police Association, said the staff members treated were two officers and two civilians.

"We don't know what the exact nature of the exposure is and because we don't know that, we don't know what the health ramifications are for those that have been significantly contaminated," he said.

After a search by fire officials, it is believed the smell was fumes from a domestic cleaning product that may have been dumped down a drain, Chaput said. Fumes from the product then got into the building's air ventilation system.

Traffic was blocked around the PSB while entrances to the building and adjacent parking lot were taped off until about noon.

Although haz-mat and fire crews left the the scene shortly after noon, officers and civilian staff from the PSB remained across the street at the Red River College campus, awaiting word that they could return to work.

The plumbing system in the building was being flushed out, Chaput said.

Staff members were finally given the clearance to go back into the building at 3 p.m.

While there were disruptions due to the incident — a small group of prisoners were moved to other police stations — the 911 emergency system is operated out of another building and was not affected by the incident, Chaput said.

2nd time this week

The PSB was also evacuated due to a hazardous materials incident on Wednesday.

Four police employees were sent to hospital for observation that day after several people inside the building had complained of nausea and dizziness.

A decision was made to evacuate at about 1 p.m. and that wasn't lifted until about 4 p.m.

However, the cause of the sudden onset of illness remains unknown. Police said they believe it was airborne.

Manitoba's department of Workplace Safety and Health is investigating.

"It's yet to be determined whether Wednesday's incident is linked to today. I know it's a similar type of event, but whether it's the same product that caused the evacuation, we're not sure yet," Chaput said Friday.