A group of Thai boys and their soccer coach have entered a brief period of monkhood to express gratitude for their rescue from a cave in northern Thailand where they were trapped for more than two weeks.

Dressed in white robes with their heads shaved, the boys were ordained at a Buddhist temple in the northern province of Chiang Rai on Wednesday for their nine day monkhood. Their 25-year-old coach will serve as a monk for three months.

While it rained, the group offered flower garlands to their parents and the widow of Saman Kunan, a former Thai SEAL diver who died during the dramatic rescue, to express regret and apologise for all their wrongdoings.

The only casualty during the rescue mission, Saman died while placing oxygen tanks inside the cave.

In Thailand, where the majority of the population are Buddhists, ordination serves as an act of gratitude. Any adult male can enter a brief monkhood, while boys can serve briefly as novices.

On Tuesday, the group participated in two ceremonies at the temple – to thank holy spirits for their rescue, and to get their heads shaved, typically done one day ahead of the ordination.

Adul Sam-on, 14, was the only one in the group of 13 – a dozen boys aged 11-16 and their coach – who did not join the ceremonies on Tuesday and will not serve as a Buddhist novice because he is a Christian.

The group visited Tham Luang-Khun Nam Nang Non Cave, 1000 kilometres north of Bangkok, on June 23. They were trapped inside as a flash flood blocked their only exit, leading to Thailand’s biggest ever rescue operation involving thousands of people from many countries.

-AAP