Heavy rainfall has stymied efforts to rescue members of a youth soccer team trapped in a cave in northern Thailand, with underground passages flooding faster than they can be pumped out.

Muddy water rising to the ceiling of one of the chambers has prevented navy divers from progressing further into the cave to where they think 12 boys and their coach, who went missing on Saturday, might be sheltering.

Thai cave rescuers consider options as search continues Read more

There has been no contact with the group since they entered the Tham Luang Nang Non cave in Chiang Rai province.

At the entrance to the cave, officials have brought in large water hoses and more water pumps. Navy divers who have been working their way through the complex said on Wednesday that water levels were rising in some places at a rate of 15cm an hour.

“We tried to pump the water [out of the chamber] but the water keeps rising. That means the water that comes in with the rain is still much more than what we can pump out,” said Narongsak Osatanakorn, governor of Chiang Rai. “So we need to pump the water faster.”

We still have hope. All agencies are trying their best. Chalermchai Sittisart, Thai general

Narongsak also said teams continued to look for another way in to the blocked portions of the cave by searching for any shafts on the mountain above that might be accessible. Two fissures were found on Tuesday but led nowhere. Rescuers are exploring another one found on Wednesday morning.

Despite setbacks, officials remained publicly optimistic about the prospects for a successful rescue.

“We still have hope. All agencies are trying their best. We have a challenge from the water level that keep rising,” Thai army chief General Chalermchai Sittisart said at the site. “We are adding more pumps to lower the level down so that the Seal team could operate better.”

He added that all agencies were working hard, “rotating 24 hours so that we can have a success in this operation”.

The US military was preparing to assist. The US Indo-Pacific Command, which is based in Hawaii, is sending a special operations team to Thailand in response to a request for help with the rescue effort, according to one US official. It wasn’t immediately clear when the team would arrive.

Facebook Twitter Pinterest People pray near the Tham Luang caves during a search for members of an under-16 football team and their coach, in Chiang Rai, Thailand. Photograph: Soe Zeya Tun/Reuters

Interior minister Anupong Paojinda said earlier the divers could proceed only when enough water was pumped out to create space between the water and the ceiling, making it safer to work. The divers will also soon start using special oxygen tanks that provide longer diving times, he said.

One diver said the water was so murky that even with lights they could not see where they were going, so they need to be able to lift their heads above the water.

The boys aged 11-16 have been missing since their 25-year-old coach took them to the cave complex on Saturday after a practice match.

The cave complex extends several kilometres and has wide chambers and narrow passageways with rocky outcrops and changes in elevation. Still, officials have said they are hopeful the boys found a safe space away from the floods.

Parents waited overnight in tents outside the cave entrance as rain poured. Medics sat in a tent nearby, and bicycles, backpacks and soccer cleats the boys left behind remained at the entrance.

Authorities have said footprints and handprints were found inside the cave complex, as well as other items thought to belong to the boys. They noted that tourists trapped there by past floods have been rescued after the waters receded.

The cave, cut into a mountainside near the border with Myanmar, can flood severely during the rainy season, which runs from June to October.