The main town on Nias, Gunung Sitoli, seems to have been largely destroyed.

ECONOMIST: Another earthquake, but no wave, strikes Sumatra

It is understood the problem began at about 19:30 GMT and all NIAS telephone land lines and computers were affected.

BBC: Communications problem at NI ambulance service resolved

For more than three hours, all of its calls were diverted to ambulance staff in Scotland, who then contacted NIAS workers via their mobile phones.

BBC: Communications problem at NI ambulance service resolved

It was felt along the length of Sumatra but, unlike the one on December 26th, did not trigger a great wave and so devastated only a relatively small area: the islands of Nias and Simeulue and neighbouring islets about 130km (80 miles) off the coast.

ECONOMIST: Another earthquake, but no wave, strikes Sumatra