A man was shot in the chest during a rally against a Constitutional Court ruling after key protest leaders were accused of trying to bring down the constitutional monarchy.

The man was shot in front of the Forensic Medicine Institute of Police General Hospital at 5.12pm and was rushed out of the area for treatment, following several gunshot sounds.

The protest was staged at Democracy Monument at 3pm and led by the United Front of Thammasat and Demonstration, the Thalu Fah Group, the Democracy Restoration Group, the Ratsadon movement, and the Coalition of Salaya for Democracy, Supporter Thailand, We Volunteer and Campaigning for a People's Constitution groups.

Afterwards, the rally moved on to Pathumwan intersection. Marchers had also intended to visit the German embassy in Sathon district to submit a petition to reform the highest institution.

However, police had already blocked the lanes in and out of Pathumwan intersection.

Protesters then blocked more traffic while giving speeches.

The group also held aloft nine straw effigies dressed in black to represent the judicial officials who ruled that Arnon Nampa, Panupong "Mike" Jadnok and Panusaya "Rung" Sithijirawattanakul aimed to bring down the constitutional monarchy.

The court had ordered them to cease all actions deemed threatening to the democratic system with the King as head of state. They burned the effigies at the intersection.

The protesters claimed that the Constitutional Court's ruling is bringing the country back to an absolute monarchy and they were opposing it.

At 6.20pm, protesters reached the German embassy to submit a statement opposing the court ruling.

Three representatives were allowed into the embassy premises to hand in the statement.

It was the second rally outside the embassy, following a demonstration on Oct 26 last year that led to the indictment of 13 leaders on lese majeste and other charges.