Red shirts protesters went berserk on Wednesday after their leaders surrendered to police and ended Rajprasong rally.
They attacked by setting fire on TV 3 Channel and library of Stock Exchange of Thailand.
One staffer said cars parked outside the building were set on fire and protesters then entered the Channel 3 building.
The fire sent thick black smoke into the air. The channel stopped broadcast, showing only channel logo as the fire start at the floor of the station.
TV reporters who were trapped inside the building telephoned their friends, complaining that no police and fire fighters came to their rescue.
The protesters also set fires at the Stock Exchange of Thailand building.