MAE SAI, Thailand (AP) — Rain is continuing to fall and water levels keep rising inside a cave in northern Thailand, frustrating the search for 12 boys and their soccer coach who have been missing for nearly four days.

At the entrance to Tham Luang Nang Non cave in Chiang Rai province, officials are bringing in large water hoses and more water pumps on Wednesday morning. Navy SEAL divers who have been working their way through the sprawling cave complex say water levels inside are rising in some places at a rate of 15 centimeters (6 inches) per hour.

A volunteer rescue worker says the navy team has been working "all night last night at the farthest chamber we can access."

Officials have previously said they believe those missing are still alive.