A St Vincent's Hospital spokesperson told Fairfax Media the woman was admitted during a "very busy night" and remained in a "critical condition" on Saturday morning, but would not provide further details.

The one-day festival at The Domain in Sydney attracted more than 28,000 people who were eager to continue partying long after the New Year's Eve fireworks.

NSW Police said they arrested 184 revellers in relation to drug offences, including eight charged with drug supply.

A 26-year-old was found to be carrying 100 ecstasy capsules, and a 19-year-old man was found with 81 capsules.

Both were charged with supplying drugs and granted conditional bail. They will appear at Downing Centre Local Court later this month.

"While most revellers were well-behaved, 184 drug related arrests shows that there are still some who think they can get away with possessing and supplying drugs," said chief inspector Stuart Bell.

"We will continue to target drugs, alcohol-related crime, and anti-social behaviour, particularly at music festivals.

Police also said 212 people were treated by paramedics, with five being taken to hospital.

Festival-goers danced to hip-hop, house, indie and electronic artists, including headline act, British duo Disclosure.

The number of drug arrests this year, fell from a record high of 214 at last year's event.

"Police will continue to run these operations and work with the festival organisers to ensure music-lovers can attend festivals and enjoy themselves in a safe, drug-free environment," said Mr Bell.

"We make no apologies for finding people who supply and possess drugs, and putting them before the courts."