The political unrest in Thailand is deepening, with a key leader of the pro-government Red Shirt movement shot and wounded outside his house in the country's north-east.

In what police believe to be a politically motivated attack, Kwanchai Praipana was shot multiple times in a drive-by shooting in his home town of Udon Thani.

His attackers have not been identified and he is being treated in hospital for a wounded arm and leg.

The shooting is likely to deepen the political unrest just a day after Thailand's prime minister Yingluck Shinawatra imposed a state of emergency in Bangkok and surrounding districts.

The government issued the 60-day emergency decree late on Tuesday (local time), handing security agencies wide powers to detain suspects, impose a curfew and limit gatherings.

Officials said it was aimed at preventing an escalation of the protests that have gripped the capital for more than two months and brought parts of the centre to a halt.

Defiant anti-government protesters have taken to the streets again saying they will not be deterred in their campaign to bring down the government.

Bangkok appeared normal and people were going about their business as usual with police making no attempt to break up the protests, including one outside a complex where Ms Yingluck was working.

But the shooting of Mr Praipana highlighted the risk of the political deadlock turning violent.

"From the way the assailants fired, they obviously didn't want him to live," his wife, Arporn Sarakham, told Reuters.

Police said they had found 39 bullet cases at the house.

Military keeps out of the fray

Mr Praipana leads thousands of pro-government supporters in Udon Thani province.

On Tuesday, he said that if the military attempted a coup, "I can assure you, on behalf of the 20 provinces in the northeast, that we will fight. The country will be set alight if the soldiers come out".

So far the military, which has been involved in 18 actual or attempted coups in the past 81 years, has kept out of the fray.

The police are charged with imposing the state of emergency, under orders from Ms Yingluck to treat protesters against her government with patience.

"We will try our best," army chief Prayuth Chan-Ocha said.

"But if any violence erupts and no-one can solve it, the troops will have to step in and tackle it. We will look after our nation with the right methods. We will not lead the nation into any violence."

Nine people have died and dozens have been wounded in violence, including two grenade attacks in the capital over the weekend, since protesters took to the streets in November to demand Ms Yingluck step down and a "people's council" be set up to bring sweeping reforms to South-East Asia's second-biggest economy.

ABC/Reuters