Jakarta  - An undersea earthquake registering 6.1 on the Richter scale struck the western coast of the Indonesian island of Sumatra Wednesday, but there were no immediate reports of injuries or damage, the Indonesian seismology agency said.

The quake struck at 1:29 pm (0629 GMT) and was centred in the Indian Ocean, 227 kilometres south-west of Bintuhan in Bengkulu province, Indonesia's National Meteorology and Geophysics Agency said.

It occurred 30 kilometres beneath the seabed, but the statement did not say if the quake was a tsunami threat.

Earlier on Wednesday, a 6.3-magnitude quake was recorded about 30 kilometres off the north coast of Papua New Guinea, the US Geological Survey said.

Indonesia, the world's largest archipelago nation, sits atop the Pacific Ocean's Ring of Fire, where the meeting of continental plates causes high volcanic and seismic activity. (dpa)