Most people are expecting the "red shirts", the broad protest movement linked to the government, to rally and are extremely concerned about the possibility of confrontation,
Many observers were sceptical when the army insisted its declaration of martial law on 20 May did not amount to a takeover. Two days later they were proved right.
There have been numerous military coups in recent decades - this is the 12th since the end of absolute monarchy in 1932.
The last coup before this one was in 2006, when then Prime Minister Thaksin Shinawatra was toppled by the army after being accused of corruption.
The army is often accused of being sympathetic to the cause of his opponents in the current anti-government movement.