Image copyright Reuters Image caption United Airlines said its flight was diverted because of "a disruptive passenger" (file photo)

A plane carrying more than 200 passengers from Chicago to Hong Kong was diverted to Alaska after two of the aircraft's toilets were vandalised with excrement, officials said.

The United Airlines flight was forced to make an unscheduled landing in Anchorage on Thursday evening due to a "passenger smearing faeces everywhere".

Police said the man, a US resident of Vietnamese origin, made no threats.

It is not clear what led to the episode taking place.

"We received a report of a passenger who had messed up the bathrooms with his own faeces," Anchorage Airport police spokesman Lt Joe Gamache said.

The passenger, a 22-year-old whose name has not been released, was co-operative and faced "no appropriate charges for anything criminal", Lt Gamache added.

The man, who made no threats and did not try to interfere with the flight crew, was handcuffed by police at Anchorage International Airport and escorted off the plane.

Police told Anchorage TV station KTUU that he was taken to a hospital for a mental health assessment after being interviewed through a translator.

United Airlines said in a statement that flight UA895 was carrying 245 people when it was diverted because of "a disruptive passenger".

Hotel accommodation was provided for those on board, the statement added.