An Ottawa building near Parliament Hill that houses the Prime Minister's Office has reopened and staff have been allowed back in after police determined that a suspicious package was not a threat.

A man was arrested earlier Wednesday after a package the size of a briefcase was reported inside the Langevin Block — an office building at 80 Wellington St., near Metcalfe Street.

Wellington Street was also closed to traffic in both directions from O'Connor to Elgin streets while members of a chemical, biological, radiological, nuclear and explosives (CBRNE) team investigated the package, but it has since reopened.

A dangerous materials robot handled the package to determine if it was dangerous, and the RCMP said the bomb disposal unit determined that the package was not a threat. 

Police explosives unit truck

An Ottawa police explosives unit truck sits outside the west door of the Langevin building across from Parliament Hill. (Tom Parry/CBC)

Man arrested outside Langevin Block

Police responded after 11 a.m. ET Wednesday after a suspicious man was reported in the area.

He was apprehended by police outside, said an RCMP spokeswoman, Const. Lucy Shorey.

The Langevin building is across the street from Parliament Hill and houses the Privy Council offices and Prime Minister Stephen Harper's office.

Harper, who also has an office in Centre Block on Parliament Hill, was not in the Langevin building at the time of the threat.

The police drama comes on a busy day on Parliament Hill.

MPs are returning for an afternoon throne speech to open a new session of Parliament after the summer break — which was extended by Harper's decision to prorogue Parliament for a month.