Greenpeace activists unfurled a banner reading "Separate Oil and State" on the Calgary Tower on Tuesday morning. (CBC)

Nine Greenpeace activists have been charged with criminal offences after an anti-oilsands demonstration on the Calgary Tower.

Some of the demonstrators rappelled from the tourist attraction on Tuesday to hang a banner attacking the relationship between the oilsands industry and government.

Some of the environmental activists opened a ground-level emergency exit door from the inside to allow other members into the facility, police investigators said Wednesday.

The group, equipped with climbing gear, then accessed the elevators to the observation deck undetected. They opened a window that led to the catwalk of the tower and set up a rigging system to rappel down and hang their banner, which read, "Separate Oil and State."

Police convinced them to remove the banner after about half an hour. Safety concerns shut down

Security concerns

Acting Staff Sgt. Abe Hammoud said there are concerns over how easily the protesters got into the tower. He said police will talk to officials at the Calgary Tower and other downtown buildings about security.

Calgary police take Greenpeace activists into custody on Tuesday. (Jennifer Lee/CBC)

"Essentially, any building could be targeted," he said. "This is an oil city and it's a very well recognized industry in this city in particular, so any of these oil companies, banks, anybody is a potential target from protesters."

Eight people were taken into custody with a ninth arrested later that evening.

All nine — ranging from 21 to 36 years old — have been charged with one count each of breaking out, and mischief to property under $5,000.

The protesters hail from Calgary, Edmonton, Grande Prairie, Alta., B.C., Quebec and Belgium.

With files from The Canadian Press