BANGKOK: At least one Thai anti-government protester was killed and 21 were wounded in a pre-dawn bomb blast Thursday inside a demonstration site in Bangkok, emergency services said.

The bomb went off at 3:28 am (2028 GMT) in front of a stage at the Government House compound, which protesters from the so-called People''s Alliance for Democracy (PAD) occupied in late August.

Twenty-two demonstrators wounded by the explosion were taken to four nearby hospitals, emergency services said. One later died and 11 were still in a serious condition, they said.

"It''s a powerful bomb, so far one has died. We are still waiting for forensic officials and for PAD permission to go into Government House," local police commander Colonel Somchai Chueyklin told media.

An emergency medical official speaking on condition of anonymity also confirmed that one man had died.

"Ten are in critical condition at (army-run) King Mongkut hospital, one serious at Ramathibodi hospital. The man died at Ramathibodi hospital," the official said.

The protesters have vowed not to leave Government House until the government, which they accuse of being corrupt and a proxy for ousted Prime Minister Thaksin Shinawatra, steps down.

There was no immediate comment from the anti-government alliance.