Police have arrested a man accused of trying to snatch an infant from a mother at a Long Island park before a bystander jumped in to help her fight off the stranger, authorities said.

The Roosevelt man's name wasn't immediately released. He's expected to be charged with endangering the welfare of a child. Officials are expected to release more details at a news conference later Wednesday.

Police say the mother was walking with her baby in a carrier across her chest, along with another child, on busy Nassau Road across from Centennial Park in Roosevelt Tuesday afternoon when a man approached and tried to grab the infant from the carrier.

A bystander who witnessed the incident told NBC 4 New York he rushed to help as the mother fought off the stranger. He said he chased the man away.

The man may have been mentally impaired, authorities said.