NEW YORK, March 11 (Xinhua) -- Two passengers were killed and three others were critically injured after a helicopter crashed into New York City's East River on Sunday, while the pilot was in good condition, officials said.

Six people including the pilot were aboard the helicopter chartered for a private photo shoot, said Daniel Nigro, the Fire Department of New York (FDNY) commissioner, in a joint press briefing with New York Police Department Commissioner James O'Neill Sunday night.

The helicopter was upside-down and submerged when emergency responders reached it.

"One of the most difficult parts of the rescue were that five people were tightly harnessed," Nigro said. "People had to be cut out."

"The pilot freed himself -- the other five did not," he said.

Three of the victims were taken to nearby hospitals in critical condition and two were pronounced dead at the scene, Nigro said, without identifying the pilot or passengers.

The helicopter is owned by Liberty Helicopter Tours and was hired for a private photoshoot, O'Neill said.

The U.S. National Transportation Safety Board is investigating the cause of the crash.

The Eurocopter AS350 went down in the waters between New York City's boroughs of Manhattan and Queens just after 7:00 p.m. local time (2300 GMT), according to the Federal Aviation Administration.

A video posted on Twitter shows a red helicopter landing hard in the water and then flipping on its side as its rotors beat the water.

Witnesses said the chopper appeared to quickly fill with water. Mary Lee, 66, told the New York Post she witnessed the crash from her apartment window.

"It's cold water. It was sinking really fast," Lee said. "By the time we got out here, we couldn't see it. It was under water."

The weather was calm at the time of the crash, with clear skies and winds at 16 to 19 km per hour, and a visibility of 16 km. The temperature of the East River was around 4 degrees Celsius.

The helicopter reported an engine failure during a mayday call to air traffic control, according to an audio posted to liveatc.net. The audio revealed that the helicopter was upside down in the water as rescue boats arrived at the scene.

The helicopter was owned by touring company Liberty Helicopters which describes itself on its website as "the largest and most experienced helicopter sightseeing and charter service in New York City."

The company has "a fleet of 10 state of the art Airbus Helicopters (formerly American Eurocopters)," according to the website. "We have been in business and flying safely for over 30 years," it says.

The skies over New York constantly buzz with helicopters carrying tourists, business people, traffic reporters, medical teams and others. Crashes are not uncommon.

In 2011, a helicopter carrying a veteran pilot and four tourists crashed into the East River, killing three tourists. In 2013, a helicopter pilot landed safely after the aircraft lost power at about 1,500 feet (457.2 meters) with four tourists on board. There were no serious injuries.