At least four people have been killed after a strong underwater earthquake struck off the Indonesian islands of Sumatra and Java on Friday, Indonesia's disaster agency said on Saturday.

Authorities urged residents living near the coast to move to higher ground following a magnitude-6.8 earthquake which struck off Indonesian island of Sumatra.

Several residents were also injured and over 1,000 were displaced, the agency said. 

The strong quake was felt in the capital Jakarta and people rushed out of high-rise buildings.

The depth of the tremor was recorded at 30 kilometers, according to the China Earthquake Networks Center (CENC).

The Indonesian geophysics agency issued a tsunami warning after the quake. The warning lasted two hours and sent people living along the coastline fleeing to higher ground.

(Cover image: Villagers stay on high ground as they evacuate after a strong earthquake hit Pasaran island, in Bandar Lampung, Lampung province, August 2, 2019./VCG photo)

(With input from Reuters)