Traces of radioactivity originating from the damaged Fukushima nuclear power plant in 2011 have been detected in a seawater sample collected near Canada's west coast, according to a radiation monitoring group.

The Integrated Fukushima Ocean Radionuclide Monitoring (InFORM) Network said Monday that it was the first time traces of Cesium 134 had been detected off North American coasts.

The isotope is characteristic of the disaster which struck the Fukushima power plant on March 11, 2011, when a magnitude-9 earthquake unleashed a devastating tsunami in Japan.

The sample, collected in February off the coast of British Columbia, contained Cesium levels "well below internationally established levels that might represent a danger to human or environmental health," InFORM said on its website.

One of the group's scientists, professor Jay Cullen from the University of Victoria, told CBC radio that computer models had predicted the arrival of the contamination at about this time.

He said the levels of Cesium 134 are about 1,000 times lower than what is regarded as safe in drinking water.

InFORM said several more years of monitoring will be needed to determine the full environmental impact of the Fukushima disaster.

The group counts scientists, representatives from non-governmental groups and ordinary "citizen scientists" among those taking part in the monitoring effort.