Dramatic cellphone video shows the sheer chaos that broke out inside a bar as the Dayton massacre unfolded.

In the recording, screaming patrons inside Ned Peppers bar can be seen diving for cover and running toward the back as gunshots ring out, the Dayton Daily News reported.

A few seconds later, armed police officers crowd the front door — their weapons trained on gunman Connor Betts, who was shot dead by cops as he tried to storm the busy bar after opening fire on the street.

Cops recovered at least 41 shell casings at the scene but said the 24-year-old’s AR-15-style rifle was capable of holding as many as 250 rounds.

Nine people were killed in the slaughter that lasted just 30 seconds early Sunday in the city’s bustling bar and entertainment district.