Six people were arrested after an illegal late-night pool party was discovered inside Hamilton's Municipal Pool complex.

It might not be wanted by the Hamilton City Council anymore, but the Municipal Pool is still in demand - as a live-in party venue for the city's homeless population.

Multiple police units, including a dog handler, were dispatched to the pools late at night on June 24, where a gathering attended by 40 to 50 people had earlier been in full swing.

Six people had been arrested and charged with unlawfully being in the council owned complex on Victoria St.

Aroha Janine Tewara Smith, 33, was one of those arrested that night. She appeared in the Hamilton District Court on Thursday, where she was facing a charge of unlawfully being in an enclosed yard or area.

Details of the situation at the pools that night were revealed in the police summary of evidence against Tewara-Smith.

A police foot patrol near the Bridge St bridge had encountered a girl going to the toilet in the bushes near the pool. She had attempted to run away, but had tripped and her clothing had become ensnared on a piece of corrugated iron, which had been used as perimeter fencing around the now-disused pools.

The police quickly found the party that had been going on inside the pool complex and at 11.40pm called in reinforcements, including a dog handler, and made several arrests.

Police prosecutor Sergeant Bill Cronin said it appeared the pools were being used as a doss house by the homeless, some of whom had brought in mattresses and bedding, a couch and even a television and radio.

At its height, up to 50 people had been partying at the pool that night.

Tewara-Smith, who according to court documents works as a sex worker, had brought leftover food given to her by a church group, which she had distributed to others at the poolside gathering.

She pleaded guilty at her appearance and was sentenced to 40 hours' community work by community magistrate Susan Hovell.

On Thursday, the couches were gone, the bedding removed and there were no signs of anyone squatting at the complex.

Dangling from the back gate was what appeared to be a relatively new padlock. Yet there were no signs of any forced entry.

The site was flanked by electric fencing, reaching metres high and with the exception of a half open door, banging in the wind at the watchhouse, there was no sign of life.

The century-old pools complex was closed in June 2012 because of structural and safety concerns.

Mathew Bayliss, council's acting unit manager for community development and leisure, said the complex was secured with an electric fence and was routinely monitored by a security firm.

There was also signs erected at the site indicating the pool was closed.

"Anyone entering the Municipal Pool will be taking a significant risk and obviously we don't want them there," Bayliss said.

"The site is secure, you have to be pretty determined to get in."

Bayliss said the alleged pool party was the first incident of its type although the complex had been hit by taggers in the past.

Council would review security at the site and increasing the amount of signs at the complex "would be a step in the right direction", Bayliss said.

"When we inspect the site if we do see any potential gaps or areas of concern, our property team is on the case quite quickly."

Bayliss did not know how the group entered the locked complex but pointed out it was only a "stone's throw" away from the Hamilton central police station.

Police could not say how the group had gained access to the complex.

Hamilton Christian Nightshelter Trust manager Peter Humphreys was surprised to hear of the party and had no knowledge of any of the city's homeless using the complex.

"I know of most places but that's the first I have heard. We do get these places crop up from time to time," he said.

It was not only those permanently homeless sleeping in the streets, but quite often others in semi-permanent arrangements, and those who have homes, would stay out and hang out with homeless friends in the city, said Humphreys.

"Sometimes people in permanent accommodation gather together as well, stay out and socialise."

City councillors voted in June this year to permanently close the complex.

Council has budgeted $10,000 a year to keep the complex secure as it decides what to do with the site.