Four people went missing on Wednesday at around noon on a training dive near Tokong Sanggol, a small island off the southeastern town of Mersing.

The group's instructor, Kristine Grodem, 35, from Norway, was rescued on Thursday.

Fishermen spotted Alexia Alexandra Molina, 18, from France, and Briton Adrian Peter Chesters, 46, at around 1 a.m. (1700 GMT on Friday) in waters off Pengerang, a considerable distance to the south of where they disappeared, Mersing district police chief Cyril Edward Nuing told reporters.

"Both individuals ... are reported to be in stable condition," he said, adding that marine police had taken them to hospital. He declined to provide more details of the rescue.

Rescuers were searching for Chesters' 14-year-old son, Dutch citizen Nathan Renze Chesters, Nuing said.

Grodem told officials the group surfaced about an hour into their dive on Wednesday but could not find their boat.

She was later separated from the others after being caught in strong currents.

The boat operator who took them to the dive site was detained after testing positive for drugs, police said.