A terrifying security breach rocked the “TODAY” show Thursday morning … a stranger breached security and stormed inside the building from the plaza before allegedly lunging at NBC host Craig Melvin.

Law enforcement sources tell TMZ … the man was asking for Al Roker after somehow slipping past security. We’re told he couldn’t find Roker and turned his attention to confront Craig in a restricted area and allegedly lunged at him while yelling the N-word at him.

We’re told the incident happened around 9 AM ET and that staff and security rushed in — and the intruder was ultimately detained and arrested. He had made his way backstage — we’re told near the dressing room, though where exactly is unclear.

A photo taken inside the studio shows Craig surrounded by several people in the aftermath of the frightening encounter.

The incident was not captured during the broadcast. Nobody was hurt. Roughly 15 minutes after it all went down, both Craig and Al were on air, and neither hinted at the drama.