Four crew were rescued and another is still missing after a fishing boat sank off the Thai coast amid rough weather.

The Sor Choknapat, with a 13.74 gross tonnage, set sail to collect crabs when it was battered by a storm around five nautical miles off the eastern province of Chanthaburi on June 24.

Rescue teams were notified by the Chanthaburi Regional Harbor office that the vessel was in distress near the Khao Laem Sadet area.

A joint team of volunteers, Marine Department personnel, and navy officers arrived to rescue the crew.

Four Cambodian nationals onboard were saved, while a Thai steersman, Somachai Chumcharoen, 65, was missing after he was separated from the group by strong waves.

Somachai's niece, Nuchjarin Chumcharoen, 30, said: 'I believe my uncle is still alive. I hope he is found soon. We are still hopeful he will come home.'

Authorities said search operations were ongoing, but the poor weather was hampering efforts.

Thailand and neighbouring countries in Southeast Asia are at the start of their annual monsoon rainy season which sees soaring temperatures followed by powerful rain storms. The rudimentary infrastructure often struggles with the deluge, leading to widespread flash floods.