Canada's Prime Minister Justin Trudeau has expressed "tremendous concern" for the pastor sentenced to hard labour for life by North Korea's oppressive regime.

Hyeon Soo Lim, pastor of Light Korean Presbyterian Church in Mississauga, was sentenced by North Korea's Supreme Court for what it called crimes against the state. The prosecution had requested the death penalty.

The 60-year-old pastor, who is in poor health, was a frequent visitor to North Korea. He travelled with colleagues to the capital Pyongyang on January 31 as part of a humanitarian mission which his family said was to support a nursing home, nursery and orphanage.

He made a televised confession to using his humanitarian projects as a cover for religious work intended to undermine the regime, and admitted aiding defectors. However, such confessions are regarded by neutral observers as usually the result of coercion and without credibility.

Trudeau noted that Canadian consular officials have not been allowed to see Lim since his detention early this year apart from during the 90-minute trial that ended with his sentencing.

"The issues of North Korea's governance and judicial system are well known," he said. "We certainly hope to be able to engage with this individual and stand up for his rights."

François Lasalle, a spokesman for Canada's Department of Global Affairs, said on Wednesday, "Canada is dismayed at the unduly harsh sentence given to Mr Lim by a North Korean court, particularly given his age and fragile health."

He added: "Mr Lim has been in detention since February and despite repeated requests, Canadian officials have not been able to meet with him to verify his health and well-being. The trial was our first opportunity to see him. This is a serious violation of the Vienna Convention on Consular Relations and the right of states to have consular access to their citizens."

Lisa Pak, a spokeswoman for the church, said that members were still hopeful for Lim's release. "As hard as the sentence was and as shocking as it was to us, there have been cases where the sentence has not been carried out," she said. However, she added that Canadian officials "are very limited in what they can do".

Lim's sentence is extremely harsh, but other foreigners sentenced to long prison terms have been released after serving much less than their sentences. American missionary Kenneth Bae served two years of a 15-year sentence before his release, while Australian missionary John Short served only a month.

However, the "crimes" of which Lim is accused are more serious and his sentence is correspondingly longer.