Indonesian rescuers were battling to free a ferry with more than 800 people on Wednesday after it ran aground on a submerged island off the country's southernmost province, a local official said.

The KM Sirimau has been marooned for two days with 784 passengers and 55 crew members on board after it got stuck along a 184-kilometer route in East Nusa Tenggara province.

As the vessel does not appear to be leaking, the rescue operation has so far focused on attempting to dislodge the ferry to allow it to continue its journey rather than evacuating everyone, according to officials.

But efforts to free the ship from the submerged island using a towboat have so far failed, the head of Maumere city's search and rescue agency told Kompas TV on Wednesday.

Authorities are waiting for a tugboat sent by state-owned shipping company PT Pelni to arrive on Thursday and if that attempt fails all passengers will be evacuated, the official added.

"The towing can only be conducted during rising tide. If this operation is unsuccessful then we will evacuate the passengers to the nearest port," Sudayana, head of the country's rescue and search agency told the broadcaster.

Marine accidents are common in Indonesia, an archipelago of more than 17,000 islands, where people rely on ferries and other boats to travel despite poor safety standards.

In 2018, about 160 people drowned when a ferry sank into the depths of one of the world's deepest lakes on Sumatra island.

And more than 300 people are estimated to have drowned in 2009 when a ferry sank between Sulawesi and Borneo.