Officials on Long Island say they are remaining vigilant to keep residents safe after an explosion rocked the Chelsea section of Manhattan on Saturday night.

Nassau County Executive Ed Mangano says Saturday's incident is a real concern, although there have been no credible threats to Long Island. Mangano is warning the public to be vigilant as authorities monitor social media, keep watchful eyes on mass transit and intensify patrols at places where large amounts of people gather, including malls.

Terrorism analyst Denis Monette, of Massapequa, says investigators are combing through evidence and looking at surveillance and cellphone videos of the explosion. He says whoever is behind the bombing had set out to instill fear.

"We live in a world where this is not going away, it's not going to change. It's going to continue, there's going to be more of it," Monette says.

Rep. Peter King (R-Seaford) says Long Island is vulnerable, and adds that he can't help but wonder if the bombing was a "test run."

Suffolk County Police Commissioner Tim Sini emailed News 12 a statement Sunday evening saying he is in close contact with the NYPD and the FBI and are monitoring the situation.

Officials are urging the public to remember the mantra of vigilance: if you see something, say something. Any suspicious activity should be reported to 911.