United States military personnel and British divers have joined the rescue team in search of the 12 children and their soccer coach trapped for five days in a flooded cave in northern Thailand as heavy overnight rains made the search complicated.

According to officials, the flood water had overflowed into a second chamber of the Tham Luang cave and forced some of the rescue divers to turn back.

The children, aged between 11 and 16, were a member of a football team. They went into the cave Saturday and were trapped when heavy rains blocked the major entrance.

Some 1,000 Navy SEAL divers, police, soldiers, border guards and officials have been mobilized for the rescue, which is in a remote and mountainous part of Chiang Rai province close to Laos and Myanmar borders.

A team of American military personnel from the U.S. Pacific Command, together with pararescue and survival specialist, arrived at the place overnight to assist rescue operations, according to the embassy spokeswoman Jillian Bonnardeaux.

“Operators are trained in personnel recovery tactics and techniques and procedures,” she told AFP.

“Essentially what they’re looking at is assessing with the Thai authorities the potential courses of action and complementing the efforts underway.”

Three British cave diving experts also made another effort at entering the cave through chimneys on Thursday after they had attempted going in through the main entrance a day before but were turned around by the rushing flood waters.

At almost six miles, Tham Luang cave is one of the longest in the Thailand and is known to be one of the toughest, even among experienced divers.