(AP) -- Authorities are increasing security throughout New York City following explosions at the airport and subway system in the Belgian capital of Brussels.

The NYPD is increasing visible presence of officers on the streets and in the subway system across the city's five boroughs. The Port Authority Police Department is stepping up security at its three major airports. It's also employing high visibility anti-terrorist patrols throughout the PATH system and the World Trade Center site.

A number of people were killed and many others were injured in the Brussels explosions Tuesday morning.

The Brussels prosecutor's office is calling the explosions terror attacks. They came just days after the main suspect in the November Paris attacks was arrested in Brussels. After his arrest, Salah Abdeslam (AHB'-dehs-lahm) told authorities he had created a new network and was planning new attacks.