SYDNEY (Reuters) - A 5.6 magnitude undersea earthquake struck 130 kms (80 miles) northwest of the South Pacific island nation of Tonga on Wednesday, the U.S. Geological Survey (USGS) said.

The quake was originally reported as 6.1 magnitude but was later downgraded by the USGS.

There were no immediate reports of damage or injuries and there was no tsunami warning issued after the quake, which struck at a shallow depth of 42 kms (26 miles). Its location was also recorded as 392 km (243 miles) west southwest of Samoa.

(Reporting by James Regan; Editing by Clarence Fernandez and Michael Perry)