More than 44,000 illegal migrants have been arrested since July last year, according to the authorities.
Police have arrested a total of 44,168 people for illegally entering Thailand through natural channels since then.
Over 30,000 of them were found in border areas and 10,000 in inner areas of the country, according to Apisamai Srirangson, assistant spokeswoman for the Centre for Covid-19 Situation Administration, adding 411 were traffickers.
Pol Lt Gen Sompong Chingduang, chief of the Immigration Bureau, said he was asked by national police chief Pol Gen Suwat Jangyodsuk to launch measures to control the arrival of Myanmar migrants who attempted to escape surging infections in their country.
Thai authorities will liaise with Myanmar officials to repatriate the migrants as Thailand has no quarantine space left, he said.
All immigration police officers, administration office workers, soldiers and medical officials agreed to the measure, he said, noting that migrant traffickers will immediately face prosecution.
Pol Lt Gen Sompong said 34 people in a room used for quarantining at the Kanchanaburi immigration bureau were found infected with Covid-19, adding they were placed in isolation away from other people and have received treatment from doctors.
The Immigration Bureau said that news of the outbreak having stemmed from four illegal migrants in the quarantine area at the Kanchanaburi office was untrue.