A high-profile marijuana activist in the early stages of a Canada-wide seed give-away tour has been taken into custody by Calgary police, along with another man, during the second stop of the tour.

Dana Larsen's goal was to give away a million cannabis seeds to Canadians to plant on public and private property as part of a multi stop tour he calls OverGrow Canada.

But police had other plans at the Calgary event, only the second stop in the tour after Kelowna.

"It is bullshit," said Travis Donald, who attended the event.

Marijuana legalization activist Dana Larsen was arrested in Calgary on April 7, 2016 for handing out cannabis seeds at his OverGrow Canada event. 0:22

"It is just a plant that people use medicinally and otherwise for thousands of years. Our government still chooses to oppress the plant that gives all these people the relief they are looking for and it is less harmful than alcohol by any means so I don't see why people are still going to prison," Donald said.

"It is unjust."

The event had been publicized and about 150 people showed up at the Days Inn on Macleod Trail South Wednesday night.

Travis Donald says police involvement wasn't needed at a cannabis seed give-away Wednesday at a south Calgary hotel. (CBC)

Larsen spoke to supporters about the history of marijuana in Canada for about an hour.

When organizers ran out of seeds, one man went out to a van to get more and was promptly taken into custody, witnesses tell CBC News.

Larsen came out to investigate holding seeds in his hand. After speaking briefly to a group of supporters that had assembled outside, Larsen was taken into custody as well.

Cindy Heemeryck, an associate of Larsen's, says she's not happy about the police intervention.

Cindy Heemeryck, an associate of Dana Larsen's, says the group has been dropping packages of seed in mailboxes to people who have made online orders. (CBC)

"I am very upset about it, I am more upset about the van being confiscated with all our goods in there," Heemeryck said.

"When I say goods, I mean packages of seeds people have ordered online … every chance we get to a mailbox we throw tons and tons and tons in there. People are waiting all across Canada for their seed packages and now the police have them seized in our van as well as some medicinal cannabis which was mine."

Police said in a release one person had been arrested at the event and that charges are pending.

"Under the Canadian Controlled Drugs and Substances Act, it is illegal to distribute marijuana in any form regardless of whether payment is provided," the release said.

Police say they will address the incident at a news conference Thursday.