Tuesday’s protest had been held to encourage legislators to approve a motion that would lead to substantive constitutional change, including measures to limit the power of the monarchy.
The protesters gathered peacefully on Wednesday at a major junction and then moved as night fell outside the nearby national police headquarters, its gates protected by razor wire and riot police.
They said they wanted to express anger at what they regarded as disproportionate use of force the previous day by police, who employed chemical-laced water cannons and tear gas against them.
It was the worst violence during months of actions by the student-led protest movement, which has staged increasingly determined rallies of thousands of people around the country.
A two-day joint session of the Thai house and senate debated seven motions for amending the constitution. Voting took place on Wednesday and the motion backed by the protest movement failed.
That motion, submitted by iLaw, the Internet Law Reform Dialogue, would have allowed all aspects of the constitution to be changed, including articles dealing with the monarchy.
The monarchy is a virtually untouchable institution that the royalist establishment and many ordinary citizens consider to be the heart and soul of the nation, and the motion had not been expected to pass.
Two motions to set up a constitution drafting committee did pass. One, initiated by the governing coalition, calls for the committee to be composed of a mix of appointed and elected members, while the other, backed by the parliamentary opposition, says all members should be elected. The motions will have to go through second and third votes after at least a month.
The other motions, mostly dealing with details of proposed changes, all failed.
Protest leaders made clear before parliament met that they would not be satisfied unless the motion submitted by iLaw passed.
According to Erawan emergency services, 55 people at Tuesday’s protest were sent to hospitals, the largest number suffering from the effects of tear gas.
It said four remained in hospital on Wednesday, including three of the six people it said had suffered gunshot wounds. The circumstances of the shootings were not announced.
Some of the injuries occurred during a brawl between the pro-democracy protesters and stone-throwing royalists who oppose constitutional change.
Police at a news conference Wednesday spoke of only two people with gunshot wounds, and said they were not responsible.
Most of Tuesday’s violence occurred when police acted against the student-led demonstrators as they tried to push their way past razor wire and other barriers to enter the grounds of the legislature on the outskirts of Bangkok.
After about six hours of chaos, a protest leader announced the end of the protest, saying the demonstrators had captured enough ground to declare they had achieved their goal of surrounding parliament.
The parliamentary session was an effort by the government of Prime Minister Prayuth Chan-ocha to take the initiative away from the pro-democracy movement, which in addition to seeking constitutional change wants Mr Prayuth and his government to step down, and to reform Thailand’s monarchy, which it feels is too powerful and lacking in accountability.