Rescuers were searching for 40 missing Indonesians including women and children on Saturday after a boat carrying them home to celebrate the end of the Islamic fasting month of Ramadan sank off Malaysia.
Two ships, four speedboats and two helicopters were dispatched to scour the seas off Malaysia's southern Johor state but were unable to spot any of those missing, said Amran Daud, an official with the Malaysian Maritime Enforcement Agency (MMEA).
The boat, thought to be carrying 44 passengers, sank in heavy seas Thursday night around 13 nautical miles (24 kilometres) off the coast, he said, adding four people were rescued on Friday.
"The accident happened two days ago so we are trying our best," Amran told AFP. "But chances (of finding more survivors) are slim."
It is thought the Indonesians chose to travel on the boat because they were working illegally in Malaysia and wished to bypass border controls on their trip home.
The boat sank roughly three hours into its journey from Tanjung Sedili on the state's east coast to Indonesia's Batam island, with its passengers hoping to return for Eid al-Fitr, the most important Muslim holiday, Amran said.
Fishermen found three of the survivors clinging onto a plastic drum in the water and alerted the authorities, who spotted the fourth man. None of the men, aged between 26 and 31, were wearing life jackets.
"Only four of those on board were rescued by fishermen and MMEA after floating 15 hours in the sea," Amran said, adding the wooden boat's condition was "questionable" based on the survivors' accounts.
He added authorities were still investigating what caused the boat to sink.
Shipping accidents off Malaysia's coast are common as thousands of people from poorer regional neighbours, such as Indonesia and Myanmar, risk journeys in flimsy boats to work illegally in the relatively affluent country.
They fill low-paying jobs shunned by locals on plantations, construction sites and in factories.
Many Indonesians try to leave the country during Ramadan to return home to celebrate Eid al-Fitr with their families. The holiday begins on Thursday.
Authorities said last month they were beefing up patrols to prevent illegal immigrants from travelling across the waterway separating Malaysia and Indonesia.
The Indonesian consulate in Johor was quoted by national news agency Bernama as offering help to illegal immigrants who want to return, saying they could be issued temporary travel documents and even get funds, urging them not to risk a boat ride.
In mid-July, an Indonesian woman died and seven people went missing after their wooden boat overturned, also off Johor state and heading to Batam island. Twenty-seven Indonesians, all without valid documents, were rescued.
Aegile Fernandez, an official with migrant labour rights group Tenaganita, urged authorities to implement "concrete measures" to stop such journeys -- including further stepping up patrols and prosecuting boatmen and officials found taking bribes to allow the trips.
"It's been happening year after year, and we have not learned from this lesson... You should not close one eye," she told AFP. "They (the migrants) are in a very vulnerable situation."
Malaysia is also a transit point for asylum seekers fleeing unrest in their home countries, such as Myanmar.
Many of them sneak into Malaysia via boat or land and then try to reach Australia in boats via Indonesia in the hope of a better life there.
Australia announced a new policy last month to send asylum seekers to its Pacific neighbour Papua New Guinea in order to discourage such journeys after a record number of boatpeople arrived in 2013 -- more than 17,300 -- and there were a spate of drownings.