PEMATANG SIANTAR (Sumatra) • Indonesian rescue workers struggled in the rain and amid 2m-high waves yesterday to look for at least 128 passengers from an overloaded ferry that sank in Lake Toba, a tourist destination in an ancient super-volcano crater on Sumatra island.

An estimated 18 people were rescued and one passenger was confirmed dead after the ferry sank on Monday evening when it was overcome by rough weather.

"Many people have reported their relatives missing," Mr Budiawan, head of the search and rescue agency based in the nearby city of Medan, said.

The search and rescue agency was sending divers to look for victims in the lake's depths, he said.

"It might take time," said Mr Budiawan, who goes by one name. He added that bodies may be trapped in the sunken vessel.

The authorities were trying to confirm the total number of passengers who had been on board the ferry, but said at least 128 people were missing.

It is believed the ferry was operating illegally, with no manifest or passenger tickets.

The scenic Indonesian lake, with an area of about 1,145 sq km, has an island in the middle which is popular with tourists. Ferries run back and forth from the island to towns on the lake's shore.

There was no word on whether any foreign tourists were among the missing.

Video footage taken from another ferry just after the incident showed people on the second boat throwing life jackets to a dozen or more people bobbing about in the water.

There was no sign of the ferry apart from what looked like an oil slick. The wooden ferry had a capacity of 60 passengers, but was overloaded and also carrying dozens of motorcycles, according to Indonesia's Transport Ministry official Sri Hardianto.

Hundreds of rescue workers, including military and police officials, were helping with the search.

The authorities also deployed an underwater robot equipped with a camera to try to find the boat, the Jakarta Post reported.

Grief-stricken relatives waited for news, including one survivor who lost hold of her child in the confusion. "It happened so quickly," Ms Juwita, who like many Indonesians goes by one name, told TVOne.

"I wanted to grab my child but I couldn't. There were three people stacked on top of him."

REUTERS, AGENCE FRANCE-PRESSE