The 14-year-old son of a British man is believed to have died following reports that he went missing on a diving trip in Malaysia. Adrian Chesters, 46, reportedly told the Malaysian coastguard his son Nathen, who has Dutch nationality, had died while they were adrift. Following a dive off the coast of Mersing, in the southern state of Johor, on Wednesday, the group surfaced but were unable to find their boat. Fishers spotted Chesters, along with 18-year-old French national Alexia Molina, in the waters of neighbouring Indonesia. They were rescued by marine police on Saturday after floating about 130km (80 miles) from where they had been diving, and were brought back to Malaysia. Nathen died before he could be rescued, Chesters told officials, with a coastguard statement citing the father as saying he died “as a result of being too weak … was unable to survive”. Chester and Molina were admitted to a Malaysian hospital in stable condition, according to local police. The group’s diving instructor, 35-year-old Norwegian national Kristine Grodem, was rescued on Thursday in waters off southern Malaysia. Grodem was training the other three, who were hoping to obtain advanced diving licences, maritime officials said. Grodem said they had been separated by strong currents. The Malaysian police have called off their search for the 14-year-old after they concluded he had drifted into Indonesian waters, informing their counterparts in the neighbouring country. Malaysia has used helicopters, a plane, boats, divers and jet skiers to search a vast area in recent days. The Indonesian authorities are expected to continue searching for the teenager’s body. The divers had been on an excursion close to a small island, Tokong Sanggol, about 15km off Malaysia’s south-east coast when the incident took place. After diving for about 40 minutes, the group surfaced but could not locate their boat. They became separated after drifting together in the powerful currents. The alarm was raised when they failed to return about an hour into the dive. The captain of the boat who took the group to the dive site has been detained after testing positive for drugs, police said. Diving activities off the coast of Mersing, where there are several popular diving locations, have been suspended. The incident happened days after Malaysia reopened its borders to foreign visitors on 1 April.