Bangkok, Jul 10 (IANS): Divers and rescue workers in Thailand on Tuesday resumed an operation to free the four remaining boys and their coach still trapped in a cave in the country's remote north.

Eight of the boys were taken out of the Tham Luang cave complex system in Chiang Rai region in the last two days of rescue operations, but the five others remain trapped on a ledge 4 km deep inside, reports CNN.

Rescuers had moved relatively quickly in order to take advantage of good weather, but heavy downpours early Tuesday could complicate their efforts.

Former Chiang Rai governor and rescue mission commander Narongsak Osotthanakorn said on Monday night that it would take 20 hours to prepare for the third operation, but he cautioned timings could change depending on weather and water levels.

The eight boys who have left the cave are being treated in an isolation ward in Chiang Rai hospital.

Doctors are monitoring them for illnesses they may have picked up in the cave.

Osotthanakorn the boys rescued are well and that those rescued Monday were in better condition than those freed the previous day.

The boys were exploring the caves on June 23 with their coach when they were trapped inside by heavy seasonal rains, CNN reported.

After they were found on July 2, officials cautioned it could take some time to get them out, but authorities decided to act with heavy rains forecast to hit the region.

The cave complex is regularly flooded during the monsoon season which lasts until September or October.