Another of seven high school students found unconscious at a Gangneung guesthouse Tuesday has regained consciousness.

Gangneung City Mayor Kim Han-geun said Wednesday that a second student undergoing treatment at Gangneung Asan Hospital showed vast improvement earlier in the morning, and was now in a condition stable enough to drink water.

The mayor said the first survivor to regain consciousness is able to engage in simple dialogue.

Five others are reportedly in intensive care units in two different hospitals, receiving treatment in high-pressure oxygen chambers.

Police on Wednesday confirmed a defect in the gas-fired boiler at the guesthouse likely caused the deaths of three of the ten seniors from Seoul's Daesung High School. They were on a trip after taking the national college entrance exam.