Rescue officials said the operation will take between two and four days to complete. 

eNCA reports the rescue chief in charge told reporters near the cave site that today is D-day and the boys are ready to face any challenges. 

The "Wild Boars" team has been trapped in a cramped chamber several kilometres inside the Tham Luang cave in northern Thailand since 23 June when they went in after football practice and were pulled in by monsoon floods. 

Their plight has transfixed Thailand and the rest of the world, with more than 1,000 journalists registered to cover the rescue staking out a small patch of muddy land at the top of a hill near the entrance to monitor the race against time.

"Everyone who is not involved with the operations has to get out of the area immediately," police announced via loudspeaker at the site on Sunday morning.

"From the situation assessment, we need to use the area to help victims."

The order to leave the site came a day after the rescue mission chief said conditions were perfect for the evacuation to begin, but also as fears mounted that expected rains could thwart the plan by reflooding the cave.

Officials did not clarify on Sunday morning whether the complex effort had started to extract the boys, aged from 11 to 16, and their 25-year-old coach.

But Osottanakorn, on Saturday suggested they would try in the coming days, even though the boys were weak and had no previous diving experience.

eNCA