Getty Images Copyright: Getty Images Tourists observe investigators in Times Square Image caption: Tourists observe investigators in Times Square

"We continue about our lives as New Yorkers," says Mayor De Blasio.

People should take comfort with the "fundamental knowledge that they are safe and the NYPD protects them," he adds.

The 18-year-old woman who died had a 13-year-old sister who is currently in hospital, officials say.