A 6.9 magnitude earthquake struck off the northeastern coast of Indonesia's Sulawesi island late on Sunday, according to the U.S. Geological Survey, prompting authorities to issue a tsunami warning for eight cities near the epicentre.

The quake struck out at sea at a revised depth of 36 kilometres and several smaller aftershocks followed, according to the Indonesian geophysics agency BMKG. There were no immediate reports of casualties.

The agency had not lifted the tsunami warning more than an hour after the quake, a spokesman told Reuters.

<a href="https://twitter.com/hashtag/Gempa?src=hash&ref_src=twsrc%5Etfw">#Gempa</a> Mag:7.1, 07-Jul-19 22:08:39 WIB, Lok:0.50 LU, 126.17 BT (Pusat gempa berada di laut 136 km Barat Daya Ternate), Kedlmn:10 Km Dirasakan (MMI) IV-V Bitung, IV-V Manado, III-IV Ternate <a href="https://twitter.com/hashtag/BMKG?src=hash&ref_src=twsrc%5Etfw">#BMKG</a> <a href="https://t.co/ZSAsOnCc3Q">pic.twitter.com/ZSAsOnCc3Q</a> —@infoBMKG

"We have not ended it because we are still monitoring the tide gauges for high waves ... though none have been recorded yet," Rahmat Triyono, a BMKG official, told Kompas TV.

Residents in some cities panicked as tremors shook buildings and authorities urged people to seek higher ground.

Some hospitals in the city of Ternate, around 130 kilometres from the epicentre, sustained minor damage and had to be evacuated, according to media.

Residents in the seaside resort city of Manado, 185 kilometres from the epicentre, said the quake was felt strongly for several seconds but no damage was reported.