The fire broke out around 2 a.m., local time, at the Dryden Hotel in the nightlife district of Olongapo City, west of Manila, CNN reported.
Jose Borlagdatan, Olongapo chief fire investigator, said the dead all had been sleeping upstairs.
All six deaths were caused by smoke inhalation, hotel owner David Fischer said.
Front desk registration records identified the three Americans as James Brigati of Kodiak, Alaska, and Patrick Burt and Joseph Valuso, whose cities of residence were not known, The New York Times reported.
Officials are investigating the cause of the fire, but Fischer said some signs pointed to an electrical fault.
CNN reported six people died in the blaze, though The New York Times said there were seven deaths. At least one victim was from South Korea.