Mass opposition protests aimed at overthrowing Thailand’s embattled prime minister turned violent on Saturday with one person shot dead and several wounded as the government called on the army to protect key state buildings.

Mass opposition protests aimed at overthrowing Thailand's embattled prime minister turned violent on Saturday with one person shot dead and several wounded as the government called on the army to protect key state buildings.

The demonstrators, who want to replace Prime Minister Yingluck Shinawatra's government with an unelected "people's council", have mounted the kingdom's biggest street rallies since political violence in Bangkok three years ago left dozens dead in a military crackdown.

The protesters are united in their loathing for Yingluck's brother Thaksin Shinawatra, a former telecoms tycoon turned premier whose overthrow by royalist generals in 2006 unleashed years of political turmoil and sometimes violent street protests.

As tensions soared in the capital, opposition demonstrators attacked a bus carrying "Red Shirt" government supporters heading to their own rally at a sports stadium in Bangkok, throwing stones and other objects, according to an AFP photographer at the scene.

Protesters also hurled bottles at police near the venue, where more than 70,000 Red Shirts were gathered.

Gunshots were later fired near the stadium, leaving one person dead and several wounded, according to police, although the circumstances of the attack were unclear.

"A 21-year-man was shot dead by two bullets to his left side," said Boonchuay Pochantong, an official at a nearby police station in the capital.

While the protesters' numbers have fallen sharply since an estimated crowd of up to 180,000 people joined an opposition rally on November 24, they have increasingly sought out high profile targets in what experts believe could be an attempt to provoke a military coup.

Demonstrators used piles of sandbags Saturday to try to climb over barriers protecting Yingluck's offices at the Government House, but were prevented by police from entering. Yingluck was not believed to be present at the time.

With the situation deteriorating, authorities announced more than 2,700 troops would be mobilised to reinforce security in Bangkok. Protesters have stormed a number of government buildings in the capital over the past week, meeting little or no resistance from police.

"We have information that there will be efforts to escalate violence in several areas," said National Police spokesman Piya Utayo.

Protest leader Suthep Thaugsuban said demonstrators would try again on Sunday to take control of Yingluck's offices.

"Tomorrow our group will enter the area of Government House," he said in a speech to supporters.

Organisers of the anti-government demo have urged people to turn out in strength this weekend in a final push before celebrations for revered King Bhumibol Adulyadej's birthday on December 5, which is traditionally marked in an atmosphere of calm and respect.