Troops fire tear gas at red shirts protesters near Lumpini Bazaar on Rama IV road on Friday at 12.15pm in a first step to disperse the protests.
The protesters in the area captured and vandalised two military fire trucks near the bazaar on Thursday night.
They ripped the cannon from its moorings and used its plastic barrel to shoot firecrackers from behind a sandbag bunker they had commandeered from soldiers.
The attempt to disperse came after Emergency Operations center's spokesman said Friday the dispersal is unavoidable.