The Canadian government has lambasted the sentencing of a pastor in North Korea to a life of hard labour as "unduly harsh", but said it may mean new opportunities for a reationship between the two countries.

Hyeon Soo Lim, a South Korea-born Canandian pastor, has been held by North Korea since February and was sentenced this week, according to North Korea's official KCNA news agency.

Canada's new liberal prime minister Justin Trudeau expressed his "tremendous concern" over the sentencing and the Canadian government said it hoped for his quick release.

However, Trudeau's government also said it hoped Lim's imprisonment would bring new opportunities for relations with North Korea.

The conclusion of Lim's trial, who had been traveling to North Korea since 1997, could finally allow Canadian officials to visit the 60-year-old pastor – and possibly secure his release, a spokesman for Canada's foreign affairs department said on Thursday.

"Our priority now is to get access to Mr. Lim. Canadian officials are... aggressively working on that as we speak, and then to work on next steps with the North Korean government with the hope that he'll be returned to Canada as soon as is possible," said spokesman Adam Barratt.

He said Canada's requests for access to Lim to check on his health and convey messages from his family and congregation have been repeatedly denied by North Korea.

Lim had been doing humanitarian work in North Korea since 1997, according to his Toronto church, the 3,000-member Light Korean Presbyterian Church.

North Korea's highest court said Lim had attempted to overthrow the government and undermine its social system with "religious activities" for the past 18 years, China's official Xinhua news agency reported.

North Korea had previously sentenced Korean-American missionary Kenneth Bae to 15 years of hard labour but released him last year after holding him for two years. Lim's church said they hope Lim's sentencing will bring similar relief.

"We hope that he knows that there is a global community who is praying for him and also working hard to secure his release. We hope that he remembers his family and congregation and how much they love him," church spokeswoman Lisa Pak said in an email.

Lim, who has lived in Canada since 1986 and is a Canadian citizen, is the only Western citizen known to be held currently in North Korea.

Both North Korea and neighboring China have clamped down on Christian groups in recent years. Last year, Pyongyang released three detained Americans, including Bae and another man who had left a copy of the Bible at a club.

Additional reporting from Reuters.