A 911 caller warned of further explosions right after the blast that rocked Manhattan’s Chelsea neighborhood and injured 29 people, The Post has learned. “I’m looking at the explosion down the block. There will be more,” the unidentified male said, claiming to be standing at 23rd Street and Seventh Avenue in the aftermath of the terrifying incident, according to law-enforcement sources Sunday.

Investigators believe the blast was the result of a home-made, pressure-cooker bomb similar to an unexploded device found later on 27th Street, sources said. In another new wrinkle, a hand-written letter, a portion of which is in Arabic, was found inside a plastic bag that held the second device, sources said. READ MORE