A man was stabbed at the Adventureland Amusement Park late Sunday afternoon following a dispute, according to Suffolk police.
Detectives say it happened in front of the "Mystery Mansion" ride just before 5 p.m.
Suffolk police say the victim is in serious condition and that one person was placed into custody.
A spokesperson said in a statement that two families "in an external dispute got into a confrontation at the park" which resulted in the victim being stabbed.
The statement went on to say that park security responded to secure the scene and called police.
It was not immediately clear what sparked the fight.
Parkgoers who spoke with News 12 had mixed reactions.
"I think it's very sad because we're here with kids. This is a children's amusement park, and families are just coming here with their kids to have a good time," said Jessie Hagelstein, of Ronkonkoma.
"It's a little unsettling, but again, it's becoming more and more not news. It's more common and expected," said Mike LaRocca, of Copiague.
The area of the park where the stabbing happened was closed while police conclude its investigation but reopened by 8 p.m.
The rest of the park operated under regular hours for the rest of Sunday night.
The spokesperson said the park will operate under regular hours on Monday as well.