Rescue teams are to drill into a network of caves in Thailand in the hope of freeing 12 schoolboys and their football coach, who have been trapped for five days by flooding.
US army troops and three British divers have joined Thai Navy Seals in the search operation, which has been hampered by heavy rainfall that has pushed up water levels.
More than 600 rescue workers have been involved in efforts to find the group, who entered the Tham Luang tunnel complex in Chiang Rai province after training on a nearby field on Saturday afternoon.
There has been no contact with the boys, aged between 11 and 16, or their 25-year-old coach since they went into the caves, which extends for several miles and has narrow passageways.
But on Tuesday Navy divers reported finding fresh footprints inside the cave system's chambers, raising hopes the group have taken refuge on higher ground.
Divers were forced to halt their search on Thursday morning after heavy overnight rainfall pushed water levels up by about 15cm (six inches) per hour, complicating efforts to squeeze through tight bends in poor visibility.
Rescue teams have also been forced to switch off industrial pumps being used to drain water due to fears of electrocution. Power supplies supplies installed this week had also been providing lighting and better communication.
With the main entrance to the cave system blocked by flooding, rescuers have been combing hilltops for shafts that may offer an alternative route in.
“We will drill down from one of the chimneys,” Thai army commander Buncha Duriyapan said.
Prawit Wongsuwan, Thailand’s minister of defence, said 30 troops from the United States Pacific Command had joined the search operation “with equipment to help penetrate the cave walls”.
Expert divers from the UK also arrived on Thursday and “went straight from the plane into the cave to make an assessment,” said Major General Buncha.
The search operation has so far been focused on four-mile (7km) route it is believed the boys and their coach took after entering the cave.
Anmar Mirza, national coordinator of the US National Cave Rescue Commission, which is not involved in the search, predicted drilling into the tunnels could take days or weeks.
He said the boys’ youth was to their advantage and they should be able to survive for four to five days without drinking water and a month without food, providing the cave is not too cold.
“The biggest concern is them getting desperate and trying to enter swift moving water,” Mr Mirza added.
Authorities are optimistic that the group are still alive, but five days without news has taken its toll on the boys’ families, some of whom have been spent nights in tents outside the cave entrance in the pouring rain.
On Thursday morning, a Buddhist monk led a prayer for a small group of relatives, many of whom were red-eyed and crying during the prayer.
“Do not worry and wait for good news,” the monk told the families.
The football team, known as the Wild Boars, regularly take part in outdoor activities led by their coach Ekapol "Aek" Chanthawong.
The boys are from schools across Chiang Rai, a province of northern Thailand.
