They say he was captured at the scene and arrested.
He has two previous drink driving arrests and is being tested to ascertain if he was under the influence.
Unfolding in one of the city's most crowded and high-profile areas, the episode instantly raised the specter of terrorism. The officials said Rojas told officers he had been hearing voices.
Rojas is believed to have driven his Honda Accord into the crowded Seventh Avenue in downtown NY, jumped the curb and started hitting pedestrians on the sidewalk. He barreled straight up the sidewalk, knocking down some pedestrians as others ran in terror, before he crashed his vehicle into protective barriers.
Other witnesses said the vehicle drove against traffic and onto the pavement before striking the pedestrians at about midday local time.
The Navy vet was arrested just last week and charged with pointing a knife at a notary, whom he accused of stealing his identity.
Rojas was due to appear in Manhattan's criminal court on Friday to be arraigned on one count of second-degree murder, five counts of aggravated vehicular homicide and 20 counts of attempted murder. The Bronx native enlisted to the US Navy in 2011 and spent two months at a naval prison in SC in 2013.
Navy records also show he spent two months at a naval brig in Charleston, South Carolina, in 2013. Details of the circumstances were not immediately available. They don't indicate why.
Thursday's mayhem began at noon on a hot, clear day that brought large crowds of people into the streets to enjoy the good weather.
"Those insane thoughts, I guess he didn't want to think them, so he was drinking, drinking, drinking".
Police identified the woman killed by the auto as Alyssa Elsman, of Portage, Michigan.
"If you didn't know her, you might think she's reserved or shy", school principal Eric Alburtus said. "She was bright. She was amusing". He said that out of an "abundance of caution", security across key locations around the city will be stepped up and major sites in the city will get additional police coverage from the anti-terror units. Rojas' lawyer, Enrico Demarco, had no comment. One, 18-year-old Alyssa Elsman, a tourist from MI, was killed while 22 others, including Elsman's 13-year-old sister, were injured.