One man, an 18-year-old, was admitted to hospital in a critical condition, with police believing he overdosed on MDMA at the Maitland event. His condition has since stabilised and he is expected to make a full recovery.

Despite the hospitalisations, and 34 positive drug searches, police said they were pleased with the behaviour of an overwhelming majority of festival-goers at Saturday's Groovin the Moo.

But local authorities did express disappointment with some people who risked their lives taking drugs and drinking excessively, despite strong warnings of the dangers in the lead-up to the event.

About 25,000 music fans from across the state flocked to Maitland Showground for the festival.

NSW Police said ahead of the event that 150 police officers, including unformed and plain-clothed police as well as the dog squad, would patrol at the festival. The warning followed the death of two young people at a music festival in Queensland last week. Dassarn Tarbutt, 24, and Ebony Greening, 22, were found dead in a tent at the Rabbits Eat Lettuce festival in southern Queensland about 9.30am last Monday from a suspected overdose.

Officers took a different tack to Groovin this year - people caught with drugs were excluded from the event, and many were issued on the spot fines of $400 rather than given court attendance notices.

Police arrested and charged a 17-year-old man who was allegedly found in possession of 54 caps of MDMA (ecstasy). He was granted conditional bail to appear at a Hunter Children's Court next month.

Port Stephens-Hunter Acting District Operations Inspector Kristin Marshall said a further nine people were handed fines, 15 were given court attendance notices and a number of youths were cautioned under the Youth Offenders Act.

With the help of five drug detection dogs, police recorded 34 positive drug searches - including illicit substances that had been dropped on the ground.

Acting Inspector Marshall said of the event's 15 hospitalisations, 14 were due to drug or alcohol intoxication while one was due to an assault. Acting Inspector Marshall said the results were "not too bad" considering the size of the crowd, but that police were disappointed that despite the warnings, some still chose to partake in dangerous behaviour.

Billie Eilish headlined the otherwise hip-hop heavy lineup featuring Hilltop Hoods, Hermitude, Duckwrth, ASAP Twelvyy and '90s throwback Coolio.

There was plenty of Aussie talent with DMA'S and Nick Murphy also heading the bill.

An overcast morning threatened rain but the clouds parted just in time for an energetic performance from local rockers Trophy Eyes.