SAN FRANCISCO, May 30 (Xinhua) -- Residents in the eastern parts of the U.S. state of Massachusetts reported hearing an extremely loud boom on Saturday afternoon, but its cause remained unclear, U.S. media reported.

NBC10 Boston reported that people across eastern Massachusetts heard the loud sound, but no one seemed to know yet what caused it.

The report cited Watertown police as saying on Facebook that they had received numerous reports of a loud boom from residents. Police said the origin was unknown and there were no reports of hazards at the time.

Coventry police in Rhode Island said there had been no reports of damage or a local incident, according to the report.

The cause of the boom remains under investigation. ■