Image caption Officials are monitoring the empty vessel in case it becomes an obstruction to other shipping

A Japanese fishing vessel swept away by the March 2011 tsunami has been spotted adrift off the west coast of Canada.

An aircraft patrolling the seas off British Columbia saw the vessel, which is about 50-metre (164ft) long, floating 275km (170 miles) from the Haida Gwaii islands on Friday.

It is believed to be the first large item from the millions of tonnes of tsunami debris to cross the Pacific.

No-one is believed to be on board the ship, registered in Hokkaido, Japan.

Canada's transport ministry is monitoring the vessel for marine pollution and to see if it becomes an obstruction.

The tsunami last March generated more than 25 million tonnes of debris,say researchers at the University of Hawaii. Between four and eight million tonnes were washed into the ocean, with one to two million tonnes still floating on the surface.

The main mass of the debris is not expected to make landfall in North America until March 2014.

Maria Cantwell, US senator for Washington state, said the boat was expected to drift slowly south.

"On its current trajectory and speed, the vessel wouldn't make landfall for approximately 50 days," Sen Cantwell said in a statement.