The Japanese coast guard rescued a pet dog on Friday that somehow survived three weeks at sea after apparently being washed away in the tsunami.

Reuters reported the dog was found on the roof of a house floating off the coast of Kesennuma, in the Miyagi prefecture in northern Japan.

The dog was described as "emaciated, but alive" after it had been adrift since the March 11 disaster.

A helicopter first spotted the dog, but the animal was scared by the propellers, so it hid under the roof. Rescuers were forced to descend onto the roof to try to lure the dog to safety. They even tried to poke a hole in the roof, but the dog still stayed away.

Eventually, the dog was saved by a coast guard boat that took over the rescue when the helicopter ran low of fuel, Japanese broadcaster NTV said.

The force hoped the dog's owner might be nearby and the dog would lead them to its owners, but no one was found in the house, the broadcaster said.