Shocking footage shows Portland Black Lives Matter protesters set office building ON FIRE and throw rocks during ‘riot’

SHOCKING footage has shown Portland Black Lives Matter protesters set an office building on fire and throw rocks during a "riot."

The demonstrators marched to the Multnomah Building on Tuesday night as authorities declared the assembly unlawful.

The building, which houses county government operation, also had its doors smashed and fires were set alight outside of the building, according to officials.

When there was a hole in the windows, flaming materials appeared to be tossed into the building leading to the office setting alight.

"@PortlandPolice has declared the gathering near the Multnomah Building a riot after individuals vandalized, repeatedly smashed first floor windows with rocks and threw burning material into an office," the Multnomah County Sheriff's Office tweeted.

Cops then cleared the area and asked the crowds to disperse.