Parliament Hill in Ottawa has reopened after a police investigation into a "possible threat" kept the Parliamentary Precinct closed for several hours Saturday afternoon.

The Ottawa Police Service (OPS) said officers responded to reports of a potential threat but found no risk to the public.

"In co-ordination with security and policing partners, officers began to clear the area, closing streets to vehicle and pedestrian traffic. Two vehicles of interest and two persons of interest were located," OPS said in a news release late Saturday afternoon. "Following an investigation, no public safety threat was identified."

OPS said the investigation remains ongoing. No other details about the persons or vehicles of interest were provided. Police did not announce arrests or charges.

According to an alert from the Parliamentary Protective Service (PPS), obtained by CTV News Ottawa, there was a "shelter in place" order due to what PPS called a "possible threat." Parliament Hill was evacuated. 

"Earlier today an alert was sent out via the Emergency Notification System (ENS) to all parliamentarians and parliamentary employees by the Parliamentary Protective Service regarding an operation which is underway with a possible threat," PPS said in a statement. "All Parliamentary buildings are in Shelter in Place until further notice and Parliament Hill has been evacuated. As the situation is ongoing, our highest priority continues to be the safety of the parliamentary community and the public. We continue to work closely with our security partners."

Wellington Street in front of the Parliament Buildings was closed from Elgin Street to Bank Street, and Metcalfe Street was closed between Albert and Slater streets, according to police.

Roads have since reopened and visitors are allowed onto Parliament Hill again. PPS gave the all clear to Parliamentary employees just after 4 p.m.

A stretch of Wellington Street in front of Parliament has been closed to vehicle traffic since the "Freedom Convoy" protest was cleared away in February, but the Hill has remained accessible to pedestrians.