Fishermen found the 3.65 metre (12-foot) drone floating off Masbate island and dragged it to shore, said provincial police chief Senior Superintendent Heriberto Olitoquit.

They had initially thought it was a bomb and alerted police about the unusual discovery, Olitoquit said.

"A technical evaluation determined that the object is one Unmanned Aerial Vehicle," Olitoquit told reporters.

Olitoquit said the drone had been turned over to the Philippine Navy, which would then conduct a thorough investigation of the drone.

"It appears to have been floating for quite some time," Captain Rommel Galang, deputy commander of naval forces in the area, told AFP.

"We will first study this drone but initially it appears to be a UAV used largely in reconnaissance."

He said it had inscriptions and a serial number that "indicate it is an American drone".

Galang said the US embassy had been informed of the discovery and local authorities would eventually turn it over to them.

A spokeswoman for the US embassy was not immediately available to comment.