MONTREAL--A Canada Post sorting centre was closed for several hours on Tuesday because of a suspicious package addressed to Luka Rocco Magnotta.

The package was discovered at 5:20 a.m. inside the sorting centre at 555 McArthur St. in St-Laurent. Four employees came into contact with a white powdery substance and were treated for what was described as "psychological reactions."

Fifteen other employees were immediately quarantined inside the building while emergency crews tried to determine what the substance was. Around 8:00 a.m. police determined that the material was harmless and allowed the building to re-open.

Accoridng to Montreal police spokeswoman Anie Lemieux, police will be investigating to determine who sent the package.

Later in the morning, a second suspicious package was found at a Canada Post distribution centre in Sainte-Julie, east of Montreal.

Just after 9:00 a.m. a worker found powder in the bottom of a mail container that had been shipped from the same St-Laurent sorting station affected by the early scare. Police evacuated the building, 30 people were decontaminated at the scene and five were sent to hospital with skin irritation.

Because of the threat, mail delivery in Sainte-Julie and Saint-Amable will not take place on Tuesday.

In the past six weeks other Canada Post offices, as well as government and media companies, have had to cope with suspicious packages. On June 18, a package with white powder that turned out to be harmless was discovered at 4290 Ontario St. E.

Two weeks prior to that, suspicious packages were sent to more than a dozen government and media buildings.

--with files from The Canadian Press.