The Bangkok Metropolitan Administration (BMA)'s Erawan Medical Centre reported bomb-like sounds were heard twice at the medical service tent at the protest site at the Government Complex around 8.30pm last night.
M-79 grenades were reportedly the source of the explosions, one falling at a footbridge over the medical service tent and another hitting a nearby temporary bathroom for woman protesters.
There were no injuries reported from the attacks.
It was believed that the grenades were fired from launcher and passing over the Department of Special Investigation (DSI) headquarters to test the path of the grenades.
At around midnight another explosion was heard at Makhawan Rangsan Bridge on Ratchadamnoen Avenue, with no injuries report.
In the western province of Ratchaburi, the office of the Democrat Party was attacked with a hand grenade but it failed to explode.