The New York Police Department has tightened security at holiday markets in New York City after a fatal truck attack at a Christmas fair in Berlin on Monday.

Members of the NYPD counterterrorism unit patrolled Christmas market in Bryant Park and the area surrounding the Christmas tree at Rockefeller Center, Union Square and Macy's in Herald Square.

At Bryant Park's Winter Village, a couple from Stuttgart, Germany who didn't want to reveal their names said they saw the attack on the Berlin holiday market on TV. "It's very, very terrible," said the wife. "I don't know what are our friends and relatives are feeling right now. Hope they are doing OK."

NYPD said in a statement that the department has moved highly trained teams, including the Critical Response Command, to high profile locations around New York City, according to New York Daily News.

Mayor Bill de Blasio said NYPD is reinforcing the Christmas market locations around the city.

"Around the holidays, from Thanksgiving to New Year's Eve, we are at a heightened state of alert, on top of our already high state of alert," de Blasio said. "And we move our assets constantly."

Hong Xiao contributed to this story.

- China Daily