Over 50 people have been hurt so far, some with gunshot wounds.

But the police denied that they had opened fire with live ammunition or rubber bullets and said they were investigating who might have used firearms.

Thousands of anti government demonstrators met outside parliament calling for constitutional change curbing the powers of King Maha Vajiralongkorn and the removal of Prime Minister Prayuth Chan.

OSHA lawmakers inside were discussing several proposals for constitutional changes, most of which left the king's powers untouched.

Protesters advanced on police with makeshift shields, including inflatable pool bucks.

Some scuffled with dozens of yellow shirted royal supporters who had staged an earlier demonstration calling on lawmakers not to make changes to the constitution.

After about six hours, police pulled back and abandoned their water trucks, which protesters then mounted and sprayed with graffiti.

The latest protests have emerged as the biggest challenge to the country's establishment in years.

Demonstrators say the Thai monarchy has helped enable decades of military domination in the country.