Four ambulances left the area around the flooded Tham Luang Nang Non cave in Chiang Rai, northern Thailand where members of the youth soccer team have been trapped for more than two weeks.

But Thai officials were tight-lipped on Monday throughout the rescue operation, and would not comment on how many people were removed.

On Sunday, when the high-risk rescue operation to rescue the 12 boys and their coach began, teams of divers brought out four of the boys but waited several hours before confirming their safe rescue.

Chiang Rai acting Governor Narongsak Osatanakorn said early on Monday that the second phase began at 11am and authorities “hope to hear good news in the next few hours”.

“All conditions are still as good as they were yesterday,” Narongsak told a news conference. “The boys’ strength, the plan – today we are ready like before. And we will do it faster because we are afraid of the rain.”

He said there were favourable factors for a successful rescue, including the fact that water levels in the cave were stable despite some heavy downpours overnight.

“Everything is all good – weather, water and the boys’ conditions,” he said, adding, “We will speed up [the operation].”

Authorities have been rushing to extract the boys, aged 11-16, and their 25-year-old coach from the cave as the annual monsoon bears down on the mountainous region. Workers have been labouring around the clock to pump water out of the cave.

Authorities have repeatedly said heavy rain could re-flood crucial parts of the cave complex that have already been drained and make the escape route much harder or even impossible to navigate.

The dangerous operation involves the boys traversing a more than 4km escape route in which they need to dive through the cave’s dark, tight and twisting passages.

The four boys pulled from the cave on Sunday were said to be happy and in good health.

“This morning they said they were hungry and wanted to eat khao pad grapao,” Narongsak said referring to a Thai dish of meat fried with chilli and basil and served over rice.

Still, they were still undergoing medical checks in a hospital in the provincial capital and were not yet allowed close contact with relatives due to fear of infections. Relatives were able to see them through a glass partition, the governor said.

Officials said Prime Minister Prayuth Chan-ocha visited all eight of the boys and made a trip to the cave for the first time since the extraction operation began.

The boys and their coach went exploring in the massive cave network on June 23 after football practice, and were cut off when a rainstorm flooded the cave. A massive international search operation was launched and it took 10 days to locate the boys, who had taken shelter on a dry slope deep in the complex.

The search and rescue operation has riveted people both in Thailand and internationally, with journalists from across the world travelling to this town along the border with Myanmar to report on the ordeal.

Interior Minister Anupong Paojinda said early on 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. He had said fresh air tanks needed to be laid along the underwater route.

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.

Sunday’s mission involved 13 foreign divers and five Thai Navy Seals. Two divers accompanied each of the boys, all of whom have only been learning to dive since July 2, when searchers found them.

Cave rescue experts have said they consider an underwater escape to be a last resort, especially with people untrained in diving.

The death on Friday of a former Thai navy SEAL underscored the risks. The diver was working in a volunteer capacity and died on a mission to place air canisters along the passage to where the boys are, necessary for divers to safely travel the five- to six-hour route.

Agence France-Presse, Associated Press, Kyodo