OFFICER SAFETY - Portland demonstrators use rope from flag to lock cops in precinct -OFFICER SAFETY -

Protesters in Portland, Ore. early Wednesday locked police inside their own precinct, prompting a plea on Twitter to let them out.

A small group of demonstrators dressed in black removed a flag from outside the doors to the Portland Police Bureau's Central Precinct shortly after 11 p.m. They used the flag cord to keep a roll-up door from opening, effectively locking people inside.

"Some individuals are tampering with the entry and exit doors. This is a fire safety hazard causing a serious safety concern for those in the Justice Center. Remove the items now!," said the early-morning tweet from the Portland Police's official Twitter account.

Demonstrators apparently took it a step further when they also locked the precinct's main doors from the outside with a U-lock and lit the flag on fire.

"The front door to Central Precinct was locked from the outside with the u-lock," another tweet read. "It had to be cut off from the outside so those inside could leave. The rope was taken by protesters from the flagpole and tied to the roll-up doors on the Southeast corner of the building."

Less than an hour later, the police tweeted again, "Locking the Justice Center from the outside presented serious life safety concerns for the adults in custody and employees inside the building. The demonstrators have moved away from the building and doors are re-opened." The burning flag injured one person, according to the police, though the person's name was not revealed.