A 23-year-old man has died after suffering a cardiac arrest at a music festival in Sydney where 14 other people were taken to hospital suffering from apparent drug overdoses.

More than 18,000 people attended the International Regatta Centre in Penrith yesterday for the annual Defqon music festival which features hard trance DJs.

In a statement, police said the 23-year-old presented to the event's medical centre about noon before his condition deteriorated and he began suffering seizures.

The man was taken to Nepean Hospital by ambulance but died last night after a series of prolonged cardiac episodes.

Police said it is understood the deceased man had travelled to the event from Victoria with friends.

A drug operation was carried out at the festival with police arresting 84 people for possession of illicit substances.

Police will prepare a report for the coroner on the man's death.

New South Wales Premier Barry O'Farrell says police are working to crack down on drug use, in an effort to save people's lives.

"This is just another demonstration that those people who call these substances 'recreational drugs' are dead wrong," he said.

"This is unacceptable."