A midair collision sent a small plane and a tourist helicopter spiraling into the Hudson River, killing at least one person Saturday as witnesses watched in disbelief.

The victim's body was found in the water off 14th St. following the crash on a clear, sunny afternoon, police sources said.

A survivor of the collision was pulled from the water by the Coast Guard, authorities said.

"I heard a noise, looked up, and seen a small plane and a helicopter just going down," recounted eyewitness Richard Martyn, who watched the crash from a West Side bike path.

"It was like a muffled boom," he said. "I'm still shaking."

There were five passengers and a pilot on the tour helicopter, operated by Liberty Helicopters, sources said.

It's unknown how many people were on the plane, which was registered to a Pennsylvania company and departed from Teterboro Airport, a police source said.

Eyewitness Scott Reynolds, 42, said the helicopter seemed to explode after the collision above the New Jersey side of the river.

"There was a white puff," said the Florida tourist. "It looked like the rotors just exploded, like something hit him."

Vern Brownell, a private pilot from Hoboken, N.J., said there was a huge bang - "like a cannon" - before the helicopter and the plane dropped like stones into the river.

"I looked over and saw two aircrafts falling from the sky," he said.

The single-engine plane "lost its wing" in the crash, he said, before spiraling into the water.

Rescue ships responded quickly to the crash site, where rescue efforts were hampered by spilled fuel oil that turned the river even murkier.

The chopper's propeller separated from its body as the helicopter plunged into the water, according to one witness.

"I just looked up, and I saw parts of the propeller in the air," said eyewitness Alanna Duffy, 29. "They were mangled."

Ambulances, fire trucks and police vehicles sped to the scene just south of 14th St. near Pier 54. Duffy said she saw police divers suiting up, and police helicopters hovered above the crash site.

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