Four more members of a Thai soccer team have been rescued from a flooded cave in the country's north on day two of a rescue mission, leaving five members of the team still inside, the Thai Navy SEALs report.

The second day of the underground rescue attempt began at 11:00am local time (2:00pm AEST) and ran ahead of schedule, according to Thai authorities.

Monday's operation took 9 hours, two fewer than Sunday, with rescuers helped by the experience they've accumulated, Mr Narongsak told a press conference punctuated with rounds of applause.

"We have more operating personnel. And we have more expertise than yesterday," he said.

But rescuing the remaining five people, which includes the boys' 25-year-old soccer coach, could take more than one operation, Mr Narongsak said.

Two ambulances with flashing lights leave the cave rescue area in Chiang Rai province. ( AP: Sakchai Lalit )

It is understood the same divers who rescued the first four boys were given the job of getting the remaining team members out.

Here's what has happened so far: June 23 — 12 boys and their soccer coach are reported missing inside Tham Luang Cave

— 12 boys and their soccer coach are reported missing inside Tham Luang Cave June 24 — Rescue mission begins

— Rescue mission begins June 25 — Thai Navy SEAL divers enter the cave to begin the search

— Thai Navy SEAL divers enter the cave to begin the search June 27 — US military and British divers join rescue efforts

— US military and British divers join rescue efforts June 28 — The underwater rescue mission is paused due to heavy rains and flooding. Pumps are brought in to drain the caves

— The underwater rescue mission is paused due to heavy rains and flooding. Pumps are brought in to drain the caves June 30 — Australian police rescue experts and Defence Force personnel join cave search

— Australian police rescue experts and Defence Force personnel join cave search July 1 — An operating base is set up deep inside the cave with air tanks and supplies

— An operating base is set up deep inside the cave with air tanks and supplies July 2 — All 12 boys and coach are found alive 4 kilometres inside the cave

All 12 boys and coach are found alive 4 kilometres inside the cave July 3 — Food and medical supplies reach the trapped soccer team

— Food and medical supplies reach the trapped soccer team July 6 — Thai Navy SEAL Saman Kunan dies during rescue efforts

— Thai Navy SEAL Saman Kunan dies during rescue efforts July 8 — 18 divers enter the cave at 10am. The first rescued boy emerges at 5:40pm. Another three follow at 5:50, 7:40 and 7:50pm

— 18 divers enter the cave at 10am. The first rescued boy emerges at 5:40pm. Another three follow at 5:50, 7:40 and 7:50pm July 9 — Divers again enter the cave system at 11am, returning with another four boys. Five remain inside.

On Sunday four boys were successfully rescued from the Tham Luang cave in a delicate and lengthy operation and taken by helicopter to Chiang Rai hospital.

The boys are reported to be in good condition, but are undergoing medical tests to check their health after swimming through dirty floodwaters to exit the cave.

"The four children are fine. The children complained that they were hungry and wanted holy basil stir-fried rice," Narongsak Osottanakorn, the head of the rescue operation, told reporters, referring to a popular Thai dish.

Health concerns include hypothermia and an airborne lung infection which is caused by bat and bird droppings.

Parents say they have not been told which boys were taken out of the cave, and have not been allowed to visit them in hospital.

At the hospital, green canvas sheets had been put up to block the entrance from view, and ambulances were on standby to receive the next batch of boys who are expected to be plucked from the cave.

Prime Minister Prayuth Chan-ocha was visiting the eight rescued boys in the hospital, Mr Narongsak said.

Dangerous journey to the surface

Australians are among about 50 foreign divers involved in the dangerous attempts to get the group to safety.

Sorry, this video has expired A 3D model of the cave complex where 12 Thai teenagers and their soccer coach are trapped.

The urgent and dangerous effort has involved the boys diving through the cave's tight and twisting passages, guided by experienced divers.

Air tanks were planted along the route earlier on Monday.

Heavy rain soaked the area on Sunday night, but the rain largely held off on Monday.

The Facebook page of the Thai Navy SEALs, who have been central to the rescue operation, was updated Monday night to say "two days, eight boars" — a reference to the Wild Boars, the name of the boys' soccer team.

The message, like most posted by the SEALs, ended with the fighting cheer adopted from the US Navy: "Hooyah".

Ambulances and helicopters have been on standby to aid the remaining boys and their coach, who have been trapped underground for more than two weeks.

An emergency team heads to the hospital in Chiang Rai. ( AP: Vincent Thian )

Sunday's rescue mission was described as a success by Thai officials.

"The operation went much better than expected," Mr Narongsak said on Sunday.

"I would like to inform the public at home and those who have been giving us support all along, after 16 days, today's the day we've been waiting for, we are seeing the Wild Boars in the flesh now."

ABC/Reuters