A team of US military personnel and British divers joined rescue efforts at a flooded cave in northern Thailand where 12 children and their football coach have been trapped for five days as heavy overnight rains hampered the search.

Flood waters seeped into a second chamber of the Tham Luang cave in Chiang Rai province forcing some of the rescue divers to turn back, according to officials.

The children, aged between 11 and 16, went into the cave on Saturday and were trapped when heavy rains clogged the main entrance.

Three British cave diving experts arrived at the scene late on Wednesday and entered the cave in full kit before emerging about an hour later.

"We've got a job to do," diver John Volanthen said as he went into the tunnel, declining to speak further.

According to the BBC, the British team is exploring possible entrances to the northern section of the cave as efforts so far have been focussed on the southern side.

With the search hampered by heavy flooding at the main entrance, the rescuers are now attempting to find other ways into the cavern complex. Experts believe there is a good chance other entrances could be concealed by thick forest.