Maria Menounos -- Car Window Explodes ... 'We're Being Shot!'

Maria Menounos thought a sniper was opening fire when her car window suddenly exploded Thursday morning in NYC -- but what really happened was still pretty scary.

One of our camera guys got Maria shortly after the accident ... and she told us shards of glass went flying everywhere because someone threw a friggin' TIRE IRON through the rear window.

The TV host was okay, but she explained how other passengers narrowly escaped serious injury.

Cops were on the scene ... but it's unclear if some tool threw the tool -- or if it was just road debris.