Although HMCS Chicoutimi's mission was scheduled a year ago, it comes after the United States and its allies agreed at crisis talks in Vancouver last month to tougher measures to halt North Korean sanctions violations, including naval security operations to prevent maritime smuggling.

The sub's mission is scheduled to last almost 200 days, with port visits in Japan and Guam. Its exact location and activities are classified.

"This deployment signals the strategic importance of the Asia-Pacific region to Canada and reinforces Canada's commitment to the maintenance of regional peace and security," Navy spokesman Captain Rick Donnelly told AFP.

The submarine, he said, was participating in "patrols and exercises with foreign navies" in the region, but will "not be doing any Olympic security" for the Winter Olympics in Pyeongchang, nor have "direct involvement" in enforcing sanctions imposed on North Korea.

Commander Stephane Ouellet told public broadcaster CBC that the sub was tasked with tracking merchant and military vessels while submerged, and observing suspicious activity including ship-to-ship cargo transfers far from ports.

North Korea has been accused of seeking to evade sanctions imposed on its isolated regime by transferring supplies from foreign vessels to its own ships on the high seas.

The sanctions are intended to restrict the North's ballistic missile and nuclear weapons development.

The last time HMCS Chicoutimi crossed an ocean in 2004, it flooded, caught fire and a sailor died. The sub did not return to operational service until 2015, after repairs and a retrofit.