An ambulance with flashing lights leaves the cave rescue area in Mae Sai, Chiang Rai province, northern Thailand, Monday, July 9, 2018. (AP/Sakchai Lalit)

Four more boys have been extracted Monday from the cave in northern Thailand where 12 members of a boys' soccer team and their coach have been trapped for more than two weeks.

Ambulances were seen departing from the cave system and arriving at the hospital in the nearby city of Chiang Rai, AP reported.

In total, eight teenage boys have been safely brought out, while five people remain inside the flooded caves.

Police and military personnel use umbrellas to cover around a stretcher near a helicopter and an ambulance at a military airport in Chiang Rai on July 9, 2018, as rescue operations continue for those still trapped inside the cave in Khun Nam Nang Non Forest Park in the Mae Sai district. (Photo: AFP/Lillian Suwanrumpha)

Four boys were rescued on Sunday night, but the mission was paused overnight to replenish oxygen supplies and make other preparations deep inside the cave complex.

According to Xinhua, the second phase of operations started at 11 am local time Monday and may take 18 hours, said Narongsak Osottanakorn, the head of the joint command center coordinating the operation.

Helicopters wait near the cave in Chiang Rai, Thailand, July 9, 2018. (Xinhua/Rachen Sageamsak)

"The factors are as good as yesterday. Hopefully we will have good news in a few hours. The rescue team is the same team with a few replacements," said Narongsak. 

The four boys rescued from the cave on Sunday night have been declared in "good overall health" though they are waiting for the results of tests. They are being treated at a hospital in Chiang Rai.

Thirteen foreign professional divers and five members of Thailand's elite navy SEAL unit on Sunday made up the main team diving the boys to safety through narrow, submerged passageways that claimed the life of a former Thai navy diver on Friday. Two divers accompanied each of the boys.

According to AP, Thai Interior Minister Anupong Paojinda had said early Monday that the same group of expert divers who took part in Sunday’s rescue would return to extricate the others because they know the cave conditions and what to do. 

Authorities have said extracting the entire team from the cave could take up to four days, but Sunday’s success raised hopes that it could be done faster.

The 12 boys, aged between 11 and 16, and their coach have been trapped in the cave since June 23. They were found when the search, joined by more than 1,000 rescuers, entered its ninth day.

Reports said FIFA President Gianni Infantino had invited the trapped Thai boys' football team to the World Cup final, as messages of support poured in from top players.

Ambulances wait near the cave in Chiang Rai, Thailand, July 9, 2018. 

(AP, Xinhua contributed to this story)