Jakarta - Indonesian rescuers Tuesday expanded their search for two Spanish men still missing after a tourist boat sank at the weekend, forcing survivors to swim hours to dry land and drink their own urine.

The boat, which was carrying 20 foreigners and five Indonesians, went down on Saturday after being hit by a storm and running into a reef as it travelled from Lombok island to Komodo island, a popular tourist destination.

Eighteen tourists and all the Indonesians onboard have so far been rescued.

The missing Spaniards had been with a first group of foreigners who were saved on Sunday after swimming for miles to a volcanic island called Sangeang, said Budiawan, Lombok search and rescue chief.

They had separated from the others in a bid to reach dry land quicker, said the official, who like many Indonesians goes by one name.

Four rescue boats and four fishing vessels joined the hunt Tuesday, which was stepped up to include the eastern side of Sangeang.

But by nightfall they had found no sign of the missing men and called off the search for the day, said Budiawan.

“Tomorrow morning we will expand the search area to include two islands near Sangeang,” he added. Local fishermen had also been asked to be on the lookout for the Spaniards.

Fishermen rescued a second group on Monday, made up of eight foreigners and the Indonesians, who were the boat crew and a tour guide.

They had floated at sea for 40 hours, with some huddled in a small lifeboat and others floating in life jackets.

Bertrand Homassel, a French survivor among the first group, told AFP how they waited for hours perched on the roof of the boat as it slowly sank.

They were eventually left with no choice but to swim to Sangeang, several kilometres away, he said. When they finally reached the small island on Saturday evening after a six-hour swim, they found it deserted.

Dehydrated, exhausted and sunburnt, they resorted to drinking their own urine and eating leaves until a passing boat picked them up the following day, he said.

The foreigners rescued were from New Zealand, Britain, Spain, the Netherlands, Germany, France and Italy.

Most of those saved have now departed Sumbawa island, where they were taken after being rescued, for either the resort island of Bali or Jakarta.

Komodo is one of several islands that make up the Komodo National Park, a protected area. Its eponymous lizards can grow up to three metres long and have a venomous bite.

Indonesia relies heavily on boats to connect its more than 17 000 islands, but has a poor maritime safety record. However boat sinkings involving foreign tourists are rare. - AFP