Paul J. Browne, the Police Department’s chief spokesman, said the helicopter had five people on board when it crashed into the East River, off 34th Street.
"The pilot and three passengers are out of the water," said Mr. Browne. "And one is unaccounted for."
Mr. Browne declined to describe the conditions of those who were taken from the water.
The age and gender of the missing person was not immediately known.
Mr. Browne said that five New York Police Department boats were on scene and that N.Y.P.D. divers were in the water, searching.
"The helicopter is submerged in an estimated 50 feet of water," said Mr. Browne.
He said the helicopter had attempted to take off moments before.
"It was departing 34th Street and appeared to have some sort of trouble and tried to come back," said Mr. Browne, who could not detail, immediately, the trouble the craft encountered.
Then it crashed.
He could not describe what type of helicopter was involved - but he stressed it was “not a tour company.””