Canada's Liberal government will introduce a law next year to legalise recreational marijuana, it said on Wednesday, fulfilling an election pledge and following several US states in permitting easy access to the drug.

Canadian Prime Minister Justin Trudeau promised during last year's election campaign that his Liberals would legalise recreational marijuana, but the time frame has been unclear. Mr Trudeau has previously admitted to smoking marijuana a few times in his life but said he never enjoyed it much.

Health Minister Jane Philpott, speaking at a special session of the United Nations General Assembly in New York, said the Canadian law will ensure marijuana is kept away from children and keep criminals from profiting from its sale.

Canadian Prime Minister Justin Trudeau promised during last year's election campaign that his Liberals would legalise recreational marijuana. AP

"We will work with law enforcement partners to encourage appropriate and proportionate criminal justice measures," she said. "We know it is impossible to arrest our way out of this problem."

The announcement came on April 20, a day celebrated by some cannabis advocates as "weed day." Hundreds gathered outside Canada's Parliament on Wednesday to smoke marijuana.