Sept 21 (Reuters) - An undersea earthquake measuring 5.7 magnitude struck off the north coast of Java in Indonesia on Thursday, the U.S. Geological Survey (USGS) said.

The quake, at a depth of 588 km (365 miles), was 125 km (77 miles) northeast of Surabaya, Java. The quake was initially measured at 6.0 magnitude.

(Reporting by Michael Perry; Editing by Stephen Coates)