A schoolboy drowned and another is feared dead after swimming at a Thai beach during a storm.

Mark and Wit, both 15, ignored the red flag weather warning to play at Chaweng Beach in Surat Thani province during a school holiday on February 26.

However, they were struck by strong waves and carried away by currents into the sea.

Their friend Tin, 15, who was also swimming at the beach, reported their disappearance to police when he noticed they failed to return to the shore.

Bo Phut Police Station officers were notified at around 6:40 pm, and officers were dispatched to conduct a search and rescue.

However, poor visibility and high waves reaching up to 2 metres tall hampered the mission.

Worried relatives waited along the shore as the Tourism Association of Koh Samui deployed speedboats to search around one nautical mile offshore.

At 9:20 pm local time, rescuers found Mark's lifeless body drifting some 1.6 kilometres from where he disappeared.

However, his friend Wit was still missing as authorities resumed the search today, February 27.

Recalling their last day together, the boys' friend Tin said: 'It was the holiday before our final exams so we decided to play football and visit the mall, before heading to the beach at around 5 pm.

'I went back to the shore at around 6:30 pm, but I noticed I returned alone.

'Mark and Wit were not strong swimmers and were not wearing life vests, so I became worried and ran to inform the adults.'

Meanwhile, Ratchaporn Poolsawadee, president of the Tourism Association of Koh Samui, reminded residents and tourists to heed safety regulations.

He said: 'Everyone must refrain from swimming at the beach when a red flag is raised due to the hazardous conditions caused by strong waves.

'Hotel operators should also play their part in warning tourists, who may not be familiar with the red flags, against swimming during these periods.'