A woman is in police custody after a suspicious package was delivered to a downtown Toronto building home to the offices of Liberal Leader Bob Rae and Ontario MPP Glen Murray, prompting a brief evacuation.

Police said an envelope containing a white powder was delivered to the constituency office on Parliament Street, north of Carlton Street, shortly after 2 p.m.

Seven employees began coughing, sneezing and itching. Police were contacted and immediately evacuated the area.

Const. Tony Vella said the package has been taken in for testing. One woman is in police custody, but no charges have yet been laid.

The employees were treated at the scene and released.

The area has been reopened to traffic.

Rae was not at the office at the time of the incident. Local MPP Glen Murray, whose office is housed in the same building, was also not at the scene.

In a statement released on his website, Murray said he was proud of the way his staff handled the scare and thanked emergency crews for how they handled the situation.

"I am grateful to the police and emergency crews for responding promptly and professionally, and for taking excellent care of my staff, whose wellbeing was and is my primary concern. I am relieved that all of them are completely safe," Murray said.

"Public service entails risk, which is borne not only by elected officials, but also by our staff. I am incredibly proud of my team, their courage and grace, and the outstanding work they do on behalf of my constituents in Toronto Centre. That work continues unabated."