They did not take phones, cash or wear watches.
When heading back to the truck they saw a security guard who told them he would sound a horn shortly to signal the locking of the gates, Ms Smith said.
After hearing a car horn sound two or three times, the pair proceeded to unpack the horses when the security guard drove past again.
"He said, 'I'm closing the gates at 8.35pm'. We said, 'Fine, we're loading up and we're on our way'," Ms Smith said.
"By the time we got down there, which would have been four or five minutes, he had secured the two big main gates, padlocked and chained them and gone."
Two other families arrived at the gates, one with a 4-year-old.
A man waiting for roadside assistance opposite the park phoned the council on their behalf, and around 20 minutes later the same security guard turned up.
"He got out of the car with a pad. I was thinking he'd write a ticket. He said, 'I'm here to let you out and there's a $40 cash fee'," Ms Smith said.
Nobody had cash and Ms Smith said the security guard spoke to his manager before informing them without cash payment he could not let them out.
He then relocked the gates and left, she claimed. The pair did not feel it was safe to leave their horses in the park unguarded, so stayed the night.
The families were collected by relatives, and left behind some food and a water container for Ms Smith and Ms Brookes.
Being made to spend the night had been frightening, Ms Brookes said, but their real concern was for the safety of the horses.
"It's an appalling attitude. We could have been overseas tourists ... we had to walk in the dark and make sure the gates were secure so the horses couldn't escape, we couldn't leave them tied up."
The friends have complained to Auckland Council and maintain the strict and severe closing time is not adequately signposted at the park entrance. But they say the worst part was the attitude of the security guard.
"We'd spoken to him, we were five minutes behind him. We were only 500 metres away from him and he couldn't be bothered coming back to say I'm actually locking the gates now," Ms Brookes said.
The guard works for Global Security, who are contracted by the council. The company referred questions to the council.
Auckland Council acting local and sports parks manager Jane Aickin said she understood a guard agreed not to toot his horn so as to not spook the horses, before waiting longer than the standard closing time before continuing his rounds. He later returned to the park and "attempted to resolve the situation".
"This was an unfortunate and unusual situation as it involved horses that needed to be able to be transported to their secure home," Ms Aickin said.
"We offer our sincere apologies to those people affected. This is not a situation we wish to see happen again."
Asked whether the guard was acting according to procedure when he relocked the gates because cash was not immediately available, Ms Aickin said the council would discuss the incident further.
"We have spoken with the contractor concerned and will be looking into this further with them to see what changes can occur to our procedures to prevent situations like this from happening.
"It is also a reminder to park visitors to check opening and closing times and allow themselves plenty of time to pack up at the end of the day."
