A pastor serving a life sentence of hard labour in North Korea for subversion is suffering ill health, according to a Canadian delegation that visited him.

Rev Hyeon Soo Lim, 61, who was the head pastor of one of Canada's largest churches, Mississauga's Light Presbyterian Church, has been held in Pyongyang since February 2015, after disappearing during a humanitarian trip to the country.

A delegate from the Seoul office of Global Affairs Canada visited Lim last week and said his health appears to be failing, according to Lisa Pak, a family spokeswoman.

Diana Khaddaj, a spokesperson for Global Affairs Canada said: "The Government of Canada is concerned for Mr. Lim's rights and well-being. We have been fully engaged on this case since it began. Consular officials are providing assistance to Mr. Lim and his family. We are grateful that we were able to visit him.

"In the interest of Mr. Lim's case, no further information can be shared."

The Lim family is hopeful the Canadian government is doing all it can to ensure the safe return of the imprisoned pastor, said Pak.

In an interview with CNN in January, Lim said he spends eight hours a day digging holes at a labour camp where he has not seen any other prisoners.

"I wasn't originally a labourer, so the labour was hard at first," Lim said in Korean through an interpreter. "But now I've gotten used to it."

The charges against Lim had lacked specifics, but Lim said it may be connected to his open criticism of the North's three generations of leaders.

"I admit I've violated this government's authority, system and order," Lim said in the interview. Asked if his biggest crime was speaking badly of the North's leaders, he said: "Yes, I think so."

Very little is known about conditions in North Korea although persecution charity Open Doors estimates at least 70,000 Christians are imprisoned for their faith.

"Christians face arrest, torture, imprisonment and death for daring to believe there is a higher authority than the nation's leader, Kim Jong-un," the charity claims.

"Many follow Jesus in secret; parents often don't even tell their children about their faith for fear they will be revealed."

For the last 14 years North Korea has topped Open Doors' World Watch List for the worst countries to live as a Christian.