Responders said Port Authority police found the man threatening to jump from the upper level of the bridge around 2:30 a.m. Sunday.
He jumped into the Hudson River about 20 minutes later, they said.
The NYPD Harbor Patrol responded during a search, which was suspended shortly before 4 a.m.
Among the questions still unanswered is how the man ended up on the upper level at that hour. The southern upper-level walkway is closed from midnight to 6 a.m. The north side walkway is always closed.
"He did not drive to the bridge," a Port Authority spokesperson said.
An investigation was continuing, she said. Until then, no further details were available.
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