BANGKOK (AFP) - Thai police shot dead a Rohingya man who escaped from an immigration detention centre on Monday (May 23) in a mass breakout in the country's south where scores of migrants are being held.

The man was killed as he threw rocks down a hill at officers scrambling to catch up with him and 20 other men who escaped after cutting through metal bars at the centre, the commander of Phang Nga province police said.

"He was throwing rocks at police from higher up the hill - that could kill the police so they had no choice but to shoot," Major General Worawit Panprung told AFP.

Two of the group of Muslim Rohingya were later caught but police are hunting for the remaining 18 who escaped early on Monday.

Southern Thailand has long been known as a nexus for lucrative smuggling networks through which persecuted Rohingya Muslims in Buddhist-majority Myanmar, and Bangladeshi economic migrants, pass on their way to Malaysia.

For years Thailand turned a blind eye to - and was even complicit in - the well-worn trafficking trade in the deep south.

It is not clear if the men who escaped were among hundreds detained in Thailand last year as the trafficking network collapsed following the discovery of mass migrant graves on the Thai-Malaysia border.

Campaigners say around 400 Rohingya - including women and children - are being held indefinitely in immigration detention centres across Thailand.

Authorities say they will release the migrants to a third country if one offers to take them.

Around one million Rohingya live in western Rakhine state, where they are forced to live in apartheid-like conditions and are denied citizenship.

For years they have fled their homeland by sea, looking for work in Muslim-majority Malaysia.