A rescue team searches for victims in the ruins of the Laurensius Say Port in Maumere, Sikka, East Nusa Tenggara after a magnitude 7.7 earthquake struck Flores Island.

Maumere, Indonesia - Rescuers combed through debris for survivors on Saturday after a powerful earthquake struck off Indonesia's eastern Flores island, killing at least 40 people, according to a disaster official.

A second strong quake was recorded thousands of kilometres away on Sumatra island in the west of the archipelago 12 hours later, but there were no initial reports of damage or casualties there.

Rescue official Fathur Rahman said the death toll from the Flores island quake had risen to 40 by Saturday evening, with 50 people injured.

Suharyanto, the head of Indonesia's national disaster mitigation agency, said earlier that people were trapped in several buildings.