Arson is being investigated as the cause of a cruise ship fire at Mitsubishi Heavy Industries Ltd.'s shipyard in Nagasaki early Sunday, the third such incident to strike in January.

According to local police and firefighters, a worker at the Koyagi plant of MHI's Nagasaki Shipyard & Machinery Works, found cardboard and insulation material ablaze aboard the 124,500-ton AIDA Prima, which is one of two ships it is building German cruise line AIDA Cruises.

Firefighters said workers quickly put out the fire and no injuries were reported.

Sunday's incident follows an electrical wiring fire near a theater space on Jan. 11, and a cabin fire involving a piece of cloth on Jan. 13.

The fires came after delivery of the ship, originally planned for March 2015, was repeatedly delayed amid design changes. The current delivery deadline is this April.