Helicopters and sniffer dogs joined the search today for three Malaysian children and their nine-year old Singaporean cousin who went missing in a hill station in Pahang, police said.

More than 100 people are looking for the four children, aged between nine and 16, who disappeared on Monday after starting a trek in the popular tourist spot of Fraser's Hill.

District deputy police chief Kamaruddin Kutik said helicopters, sniffer dog and ground parties including local residents were combing the area for the children.

The search, which began Monday afternoon, was temporarily suspended Tuesday evening due to bad weather, but has now resumed and expanded from the location of the hiking trail.

"We are going to continue day and night. We won't take any chances because it's the third day they've been missing," Kamaruddin, who is leading the operation, told AFP .

Brothers Chew Ser Yee, 16, Chew Ser Han, 14, and Chew Ser Meng, 12, from Perak state and their Singaporean cousin Jeremy Tio, 9, started their holiday in Fraser's Hill on Sunday.

Empty water bottle

The four children, armed with only a map and some water, started along a well-known hiking trail at noon on Monday. They were to be picked up later by their uncle at a pre-arranged spot but never turned up.

The only clues to their whereabouts were an empty water bottle near the trail and some footprints on a separate but closed track diverging off the boys' original path, media reports said.

"We believe they are still in Fraser's Hill," Kamaruddin said.

This is the second time in recent months that someone has gone missing in Fraser's Hill. In March, a British botanist got lost while trekking but was found five days later.