Indonesian rescuers searching for three divers, including a Singaporean, have extended their search until Tuesday.

Despite progressively widening the search area since the three went missing last Sunday, no signs of them have been found so far.

Mr Muhammad Zaenal Arifin, chief of the Banten chapter of the National Search and Rescue Agency (Basarnas), said the search was expanded yesterday to an area of 1,800 sq nautical miles in the Sunda Strait between Sumatra and Java islands.

Yesterday was the seventh day of the search operation.

"There's still no gain. We will lengthen the search for three days," he told The Sunday Times.

"During the extended period, we will focus our search on locations where our effort was not optimal."

The Indonesian rescue team totalled 180 personnel yesterday. They deployed four helicopters, including two chartered by the families of the missing divers, to help 19 divers working underwater, according to Basarnas.

The missing trio are a Singaporean identified as Mr Wang Bing Yang and two Chinese nationals, Mr Qin Xue Tao and Mr Tian Yu. They were among six foreign tourists who went diving last Sunday in two groups.

They began diving around 1.30pm local time, but only one group returned to the surface at about 2.45pm, Basarnas had said.

The trio did not return to base on Sangiang island in Banten province, adjacent to Jakarta.

The Sunda Strait, where the island is located, has strong undercurrents which have swept away divers previously.

Accidents, particularly boats capsizing, have also occurred in the area because of high tides.

On Sept 8 last year, Jakarta resident James Ade Ignatius Salaka went diving off Sangiang island, and was swept away by an unexpectedly strong undercurrent. The 32-year-old was later found dead.