The number of students who have fallen ill from salmonella poisoning at a Chiang Mai school has risen to 460.

Health authorities told the Bangkok Post the students fell ill after eating three-day-old boiled eggs.

Dr Pornthep Siriwanarangsan, director-general of the Disease Control Department, said Chiang Mai Welfare School students became sick after eating donated eggs that were boiled three days previously and not reheated before they were consumed, allowing the bacteria to develop.

Of the 460 sick,, 290 are recovering at home, 123 are still in nine hospitals, and eight students are critically ill.

Another 47 students are being treated at the school’s gym, which has been turned into a field hospital as there are not enough hospital beds available to accommodate all the sick students.