BANDA ACEH, Indonesia - Rescuers are searching for seven people, including four Australian tourists, who went missing when their boat hit bad weather off Indonesia's Sumatra island, officials said Monday.

Two boats carrying a total of 17 people left Nias island headed for the private island of Pinang on Sunday, local search and rescue agency head Octavianto said, before bad weather hit.

One of the speedboats, with 10 people on board, took shelter on another nearby island but the other boat carried on.

Rescuers were told by resort management on Pinang early on Monday that the second boat, which carried the four Australians and three Indonesians, never arrived, said Octavianto who, like many Indonesians, uses only one name.

He told AFP a search was launched immediately.

"From morning until now, we have yet to find the speedboat which carried the seven people," Octavianto told AFP.

"We will continue the search until tonight. If there is no result, the search and rescue team will be deployed again tomorrow at 0700."

The second boat, which carried another eight Australians and two Indonesians, reached Pinang late on Sunday, he said. Two rescue vessels and an aircraft were assisting the search.

The Australian Department of Foreign Affairs and Trade said it was working closely with Indonesian authorities.

"Our thoughts are with the family and friends of those missing during this distressing time," a spokesperson said.

Marine accidents occur frequently in the Southeast Asian archipelago nation of around 17,000 islands, where people rely on ferries and small boats to travel despite poor safety standards.

In 2018, more than 150 people drowned when a ferry sank in one of the world's deepest lakes on Sumatra island.

A ferry carrying more than 800 people ran aground in shallow waters off East Nusa Tenggara province in May 2022 and remained stuck for two days before being dislodged. No one was hurt.