Hazardous materials investigators are searching a Canada Post distribution centre in Montreal after overnight workers discovered a suspicious package.

An envelope with white powder inside was discovered at 3:00 a.m. Monday at the distribution centre at 4290 Ontario St. East.

The five employees inside the building at the time were immediately quarantined and as of 7:30 a.m. have not been allowed to leave.

Workers showing up to begin daytime shifts were not allowed inside the building, neither were trucks bringing the day's mail and packages to the centre.

Two weeks ago more than a dozen suspicious envelopes containing white powder were sent to government and media offices in Montreal and throughout the province. All of those packages were determined to be harmless and were sent from a group calling itself the Force armee revolutionnaire du Quebec.