Twenty-five others were taken to a hospital in relatively good condition.

Firefighters and paramedics were called to the school about 8:45 this morning, said Honolulu Fire Capt. Kenison Tejada.

"The complaints we are hearing is respiratory distress and nausea," Tejada said. "That is what they are being treated for, mostly."

The serious patients were taken to St. Francis Medical Center-West. Those in good condition were taken to Kapi'olani Medical Center at Pali Momi as well as St. Francis, said Donnie Gates, assistant chief of emergency medical services.

Most of the cases came from rooms in the school's Building C, which the principal ordered evacuated, Tejada said. Then the principal evacuated the whole school.

Firefighters then decided to check the entire campus and see if they could find the source of the problem.

"We don't know if some cloud passed through the school or what," Tejada said. "They don't use gas at the school. We called the gas company to see if they had been doing any kind of work in the area, and they said negative."

Greg Knudsen, a spokesman for the state Department of Education, said students were taken to the library on the school's lower campus and were being sheltered there, but that classes had not been canceled for the day.

Knudsen said the school experienced a similar problem in the past, one that was later attributed to a neighbor spraying chemicals in his yard.