More than 50,000 security personnel are fanning out across Bangkok as authorities brace for a three-day protest that starts later today.
The red shirt supporters of ousted prime minister Thaksin Shinawatra will begin arriving in the Thai capital today.
They aim to have a million people on the streets by Sunday and say they will stay until they topple the government.
The protesters want new elections which they believe will be won by parties allied with the red shirts.
Thailand’s cabinet has enacted strict new security laws that give the army the role of policing the city.
Travel warnings have been upgraded for Australian tourists who are being urged to avoid certain parts of the city, including the famed tourist strip Khao San Road.
There have been a number of small grenade attacks in Bangkok in recent weeks and Thailand’s prime minister is considering sheltering in a safe house until the protests are over.