Dr Narong Sahamethapat, permanent secretary for public health, said 32 protesters were injured in the clash, which lasted from 7.30am to 11am. Twenty-five of them were admitted to Ratchawithi Hospital, five to Ramathibodi Hospital, one to King Mongkut Hospital and one to Phayathai Hospital.
Most of them were suffering the effects of tear gas and rubber bullets.
One of them was hit in the head by a bullet from a firearm. He was among those admitted to Ratchawithi Hospital. His latest condition was not yet known.
Pol Maj Gen Piya Uthayo, the Capo spokesman, said three policemen were wounded. One of them, Pol L/Cpl Thanapol Nopluay, a riot policeman of the Crowd Control Division, was hit with a gun bullet in the right shoulder.
A previous report said four policemen were injured.
The Capo spokesman said the protesters threw molotov cocktails and firecrackers and fired metal nuts from catapults at the police.
An investigation would be launched and legal action taken against the protesters, Pol Maj Gen Piya said.