A helicopter crashed into the Hudson river in New York on Thursday, police said without confirming any fatalities, as marine emergency responders attended the scene.

Images showed the chopper's landing skids protruding from the river beside Manhattan's West Side Highway as several boats clustered around the impact site.

At least four people were retrieved from the water and taken to hospital in New Jersey, the NBC4 broadcaster reported citing law enforcement at the scene.

The river is a busy shipping channel and was the scene of the dramatic 2009 incident when a US Airways aircraft safely landed in the water with all 155 people on board escaping with their lives and was dubbed "Miracle on the Hudson."

"Due to a helicopter crash in the Hudson River, in the vicinity of the West Side Highway and Spring Street, expect emergency vehicles and traffic delays in the surrounding areas," the New York Police Department wrote in a statement.

A fire service spokesperson said that "we got the call at 3:17 pm (1917 GMT)" about a "helicopter in the water", but was unable to give other information.