Mayor Bill de Blasio says Baltimore's mayor and police officials are doing a good job handling the unrest and says the city remains vigilant to keep police and communities safe.
But he says protesters must act peacefully if they want to see change.
"Those individuals who committed violence in the last 24-48 hours, or any individuals who assault a police officer are denigrating any possible notion of how to improve the situation, or bring police and community together or get justice for anyone," De Blasio said.
The mayor also said he has not heard any threats against law enforcement in New York.
Meantime, the City of Baltimore has imposed a week-long, overnight curfew following a day of violent protests over the death of a man in police custody.
Fires burned through buildings and cars around the city Monday night.
Maryland's governor declared a state of emergency in Baltimore and activated the National Guard.
Officials with the Maryland National Guard say up to 5,000 troops are available to patrol the streets.
Earlier in the day, looters were seen entering several businesses, destroying cars, and taunting police.
Authorities say police were attacked with rocks and other debris.
At least 15 officers were injured, including one who was knocked unconscious.
Newly sworn-in U.S. Attorney General Loretta Lynch has condemned the violence.
Baltimore's police commissioner said he was disappointed and embarrassed by the protesters' actions.
"This is not protesting. This is not your First Amendment rights. This is just criminal acts doing damage to a community that is challenged in some ways, that do not need this and do not need to be harmed in the way that we have today," said Baltimore Police Commissioner Anthony Batts.
The unrest came after the funeral for Freddie Gray.
He suffered a spinal injury while being arrested by police earlier this month and later died.