"Today is the D-day. The boys are ready to face any challenges," Chiang Rai Governor and rescue chief Narongsak Osottanakorn told reporters near the cave site as the threat loomed of monsoon rains causing more flooding in the cave and blocking off a rescue bid.
Thai authorities told media earlier today to leave a camp site near the cave where 12 boys and their coach have been trapped for more than two weeks so that "victims" could be helped, possibly signalling a rescue effort to get them out.
Narongsak said the first boy was expected to be brought out of the cave by around 9pm (1400 GMT), meaning the trip would take around 11 hours.
Authorities earlier today told the more than 1,000 journalists who had converged near the cave site's entrance to clear the area in preparation for the rescue operation.
"Everyone who is not involved with the operations has to get out of the area immediately," police announced via loudspeaker at the site this morning.
"From the situation assessment, we need to use the area to help victims."
The "Wild Boars" team has been confined in a cramped chamber several kilometres (miles) inside the Tham Luang cave complex since June 23, when they went in after football practice and were hemmed in by monsoon floods.
Their plight has transfixed Thailand and the rest of the world, as authorities have struggled to devise a plan to extract the boys and their coach through twisting, narrow and jagged passageways that in some places are completely flooded.
The boys, aged from 11 to 16, and their 25-year-old coach were found by British cave diving specialists nine days after they ventured in, dishevelled and hungry, on a ledge several kilometres inside the cave.
But with some of them unable to swim and having no scuba experience, Narongsak had previously dubbed the rescue effort "Mission Impossible"
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.
Even earlier today officials did not clarify whether the complex effort had started to extract the boys, aged from 11 to 16, and their 25-year-old coach.
But the head of the mission, Chiang Rai Governor Narongsak, yesterday suggested they would try in the coming days, even though the boys were weak and had no previous diving experience.
"Now and in the next three or four days, the conditions are perfect (for evacuation) in terms of the water, the weather and the boys' health," Narongsak told reporters.
"We have to make a clear decision on what we can do."
Sustained heavy rains could make the water rise to the shelf where the children were sitting, reducing the area to "less than 10 square meters", he added.
Torrential rain pounded the area for around half an hour on Saturday night, highlighting the urgency. Occasional light showers continued through the night but on Sunday morning there was no rain.
However, heavier rain was forecast to return from early afternoon and persist for several days.
- Rescue options -
The death of a former Thai Navy Seal diver who ran out of oxygen in the cave on Friday underscored the danger of the journey even for adept professionals.
Yesterday another 10 members of the rescue mission -- part of a team assigned to explore the mountain to look for chimneys that might lead to the cave -- were injured when a car they were travelling in fell off a cliff.
Their injures were not believed to be serious.
The footballers were found by British cave diving specialists nine days after they ventured in, dishevelled and hungry, on a ledge several kilometres inside the cave.
But initial euphoria over finding them alive quickly turned into deep anxiety as rescuers struggled to find a way to get the footballers out of the flooded cave complex.
Rescuers had fed a kilometres-long air pipe into the cave to restore oxygen levels in the chamber where the team was sheltering with medics and expert divers.
More than 100 exploratory holes had also been bored -- some shallow, but the longest 400 metres deep -- into the mountainside in an attempt to open a second evacuation route and avoid forcing the boys into a dangerous dive through submerged tunnels.
Yesterday Thai Navy SEALS published touching notes scrawled by the trapped footballers to their families, who had been waiting for them agonisingly close by outside the cave entrance.
The boys urged relatives "not to worry" and asked for their favourite food once they were safely evacuated.
In one, Pheerapat, nicknamed "Night", whose 16th birthday the group were celebrating in the cave when they became stuck on June 23, said: "I love you, Dad, Mum and my sister. You don't need to be worried about me."
The site near the cave's entrance had swelled with media, volunteers and onlookers since the operation started, and authorities' patience has worn thin.
Mission chief Narongsak said in recent days that medic teams had complained about the media presence and they told him "it will be a problem if they have a real emergency situation".