It would have been about 40 hours since the boat carrying 22 Singapore dragon boat racers capsized in the river on Friday.

Singapore naval divers will be using sonar equipment to comb the Tonle Sap River near the Cambodian capital of Phnom Penh, together with local rescue workers.

According to eyewitnesses, survivors and race officials, the Singapore team was making its way back to the starting point, after the race, when the tragedy occurred.

Instead of waiting for a boat to tow them back, the team had decided to row towards shore themselves.

When they were close to shore, a wave hit them, causing the boat to collide with a pontoon and overturn. Team members were sucked under the pontoon. Seventeen racers surfaced and five did not.

The missing five are: Jeremy Goh, 24; Stephen Loh, 31; Reuben Kee, 23; Poh Boon San, 27 and Chee Wei Cheng, 20.

It is believed that a combination of strong currents and fatigue after the race could play a part in the likely drowning of the five men. They could also have been knocked unconscious when the 500kg boat capsized in the 9m-deep water.

The racers were not wearing life jackets.

One survivor who declined to be named said the team panicked under water and the current was pushing them down, so they all kicked their way upwards. He was treated for bruises on his face.

Eyewitness Joey Paraiso said on television last night that the current was strong. 'It happened so quickly. The Singaporean rowers, one by one, floated and saved themselves. There were some railings that they were able to hold on to.

'They were not able to swim normally, so they just looked for something to hang on to... The current was a bit strong,' he said.

The race was held to celebrate Cambodia's Water Festival, which takes place each year at full moon to celebrate the changing of the Tonle Sap River course.

This year, more than 1 million people were expected to attend the three-day race, which is Cambodia's biggest annual event. There were 432 participating boats.

Prime Minister Lee Hsien Loong yesterday expressed his sadness at the accident.

'I share the deep concerns of the families of the five Singaporeans. The Singapore Government will do all it can to provide the necessary assistance,' he said in a statement.

Speaking to reporters yesterday, Minister for Community Development, Youth and Sports Vivian Balakrishnan said: 'Our priorities are to find the missing, to provide comfort to family members and then find out what happened.'

Relatives of the missing men flew to Phnom Penh yesterday afternoon. On arrival, they went to the site of the accident before going to a hotel to be briefed on rescue efforts.

A brother of missing racer Jeremy Goh, who declined to be named, said Jeremy left for Cambodia on Thursday and was due back tomorrow.

He said at Changi Airport yesterday: 'We're just going there to see what's going on and hoping for the best.'