Canada has became the first major world economy to legalise recreational cannabis, kick-starting a nationwide experiment in drug laws and regulations despite uncertainty about the consequences.

Weed enthusiasts celebrated the "end of prohibition” as the clock struck midnight on Tuesday evening and the first legal pot sales for non-medical purposes were made across the country.

Justin Trudeau, the Canadian prime minister who pledged the change in his 2015 election campaign, tweeted that the policy would take “profits out of the hands of criminals” and protect children.

On Wednesday, his government also announced moves to make it easier for people convicted for carrying small amounts of marijuana in the past to obtain a pardon, waiving the $631 Canadian dollar fee.

However legalisation was not universally welcomed, with one leading Canadian medical journal warning the “uncontrolled experiment” would put profits ahead of the nation’s health.

And there was speculation about the impact the change could have on other nations, including America – where some states have legalised recreational use – and even Britain, where it remains a crime.