A strong 6.6-magnitude undersea earthquake rocked Indonesia's northern Maluku province on Tuesday, the meteorology agency said, prompting concerns of a tsunami.
The agency urged residents on Bacan island to be alert for signs of rising sea levels, after the quake struck 48 kilometres northwest of the beachside town of Labuha at 5:04 pm.
It said there was a risk of a tsunami because the earthquake was shallow, striking 18 kilometres under the seabed.
"Because of the magnitude as well as its shallow epicenter, there is a potential for a tsunami," said Fauzi from the agency's headquarters here.
He said there were initial reports that the quake was strongly felt in Labuha but there were no immediate reports of damage or casualties.