The Thai army has fought running battles with protesters in the capital Bangkok in a bid to end days of mass demonstrations and political chaos.
A BBC correspondent saw soldiers fire hundreds of live rounds, some into the crowds of protesters, in a bid to clear them from a major road junction.
The protesters responded by hurling petrol bombs and driving buses they had commandeered at the lines of troops.
Dozens are reported to have been wounded in the clashes.
The red-shirted protesters - thousands of whom are gathered outside the parliament buildings - have vowed to stay until Prime Minister Abhisit Vejjajiva resigns.
Mr Abhisit, who declared a state of emergency on Sunday, has appealed for calm and says his government is trying to ease the tense situation.