One woman has died, another is in an induced coma and almost 70 revellers were charged with drug offences at the Stereosonic music festival at Sydney Olympic Park.

Police say a 25-year-old woman from Oyster Bay became seriously ill during the festival on Saturday and later died in Concord Hospital.

A 22-year-old woman, believed to be from Britain, was taken to Westmead Hospital in a critical condition and placed in an induced coma. She was in a serious but stable condition on Sunday.