See this link from the BBC. Martial Law has been imposed in Thailand and the Prime Ministers office has been surrounded by tanks.
All troops have been told to report to barracks and no troop movements are allowed unless they have been authorised by the coup leaders. The armed forces are claiming that the takeover is only temporary and that power will be handed back to the people. The army say that it is necessary because Thaksin Shinawatras government has divided the country and corruption is rife.
Elections were due later in the year following the failed elections earlier this year and the military appear to have taken the chance to act whilst Thaksin Shinawatra is out of the country at the United Nations in New York.
The military state that the Council of Political Reform has taken over with the King as head of state. The position of the king in all of this will be absolutely critical to the success or otherwise of the coup.
Sadly I predicted here that the military might take matters into their own hands. However, I also predicted that the stance of King Bhumibol would be critical and I stand by that judgement now.