Some 178 people are missing from a ferry sinking on Monday at a popular lake on the Indonesian island of Sumatra, a much higher number than previously believed.

The wooden vessel, overcrowded with passengers and motorbikes, did not have a manifest and disaster officials have several times raised the number of people it was carrying as family members who rushed to Lake Toba in northern Sumatra provided information.

Only 18 survivors have been found - in bad weather within hours of the sinking on Monday evening. It is possible many of the victims were still inside the sunken ferry, said North Sumatra province police chief Paulus Waterpau.

"Many survivors told authorities that less than half of them had jumped into the water before the boat sank," he said.

Suwarni, whose 20-year-old son and his girlfriend were on the ferry, criticised the search and rescue operation as slow and insufficient.

"Millions of questions keep me from sleeping," she said.

"What kind of government is this which can't protect their own people from unnecessary accidents? And after the accident they're not able to find the victims."

"I beg help to everyone to quickly find my son and his girlfriend, even if their remains, please find my son, return him to me," Suwarni, who uses only one name, said.

Divers were searching at depths of 25m (82ft) and will deploy an underwater drone to 200m (656ft) below the surface, Mr Waterpau said.

The search and rescue effort involving 350 personnel and at least half a dozen boats has turned up items of clothing, bags and traces of oil from the ferry but just several victims.

Hisar Turnit, a spokesman for the search and rescue agency in nearby Medan, said three deaths were now confirmed after two more bodies were found on Wednesday morning.

An Associated Press reporter saw one body being transferred to an ambulance onshore.

A rescuer, who did not give his name, said the dead woman was found about four miles from where the boat sank.

Mobile phone video released earlier in the week by the National Disaster Mitigation Agency showed the crew of another ferry attempting to rescue people struggling in the waters shortly after the sinking but being hampered by bad weather and rough waters.

The 1,145-sq km Lake Toba, formed out of an ancient super volcano, is a popular sightseeing destination on the island of Sumatra.

The disaster has cast a tragic pall over holidays marking the end of Ramadan when tens of millions of Indonesians return to their hometowns.

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