Thailand's political crisis is set to enter a tumultuous new phase on Monday with the planned "shutdown" of Bangkok by opposition protesters seeking to prevent upcoming elections.

It is the latest chapter in a long-running conflict between supporters and opponents of fugitive former premier Thaksin Shinawatra, who remains a hugely divisive figure more than seven years after he was ousted in a military coup.

The demonstrators say they will block major intersections, stop officials going to work and cut off power to key state offices until they topple the government of Prime Minister Yingluck Shinawatra -- Thaksin's younger sister.

Schools will close because of fears for students' safety, while the US embassy has advised stockpiling a two weeks' supply of food, water and medicine.

The authorities say they are ready to declare a state of emergency if there is fresh unrest, and roughly 20,000 police and soldiers will be deployed for security.

At their height, the protests have drawn more than 150,000 people accusing Yingluck's government of corruption and urging her to step down.

Eight people, including a policeman, have been killed and dozens injured in street violence in recent weeks, and the government has voiced fears of more bloodshed.

"That is what they are trying to do -- to create violence during the shutdown," Deputy Prime Minister Surapong Tovichakchaikul told reporters.

Yingluck has called an early election for February 2 to try to resolve the crisis, but the opposition -- which has not won an elected majority in about two decades -- is boycotting the vote, raising fears of prolonged deadlock.

The protesters want an appointed "people's council" to run the country and oversee vaguely defined electoral reforms before new elections are held in around a year to 18 months.

Pro-government "Red Shirts" will also stage their own marches on Monday in central and northern Thailand to call for the election to go ahead, raising fears of possible confrontation between the rival factions.

'A fight to the end'

At the movement's rally site near the government headquarters, former soldier-turned-protester Anan Jandontree has produced about 1,000 homemade flak jackets filled with layers of used hospital X-ray film in preparation for the showdown.

"We will fight our best, because we have made all these, so we will fight and we will succeed," he said.

Thailand has been periodically shaken by political bloodshed since Thaksin was deposed by royalist generals.

The billionaire tycoon-turned-politician fled the kingdom in 2008 to avoid a jail term for a corruption conviction that he says was politically motivated.

He remains hugely popular in the northern half of the country, and Yingluck's Puea Thai party is expected to win the election if it goes ahead.

His sister is under pressure on several fronts: the army chief has repeatedly refused to rule out another coup, while dozens of her MPs face impeachment in connection with a bid to make the upper house fully elected.

If found guilty they could be banned from politics for five years.

"I don't think the election is going to take place because those who are in the judiciary are mostly siding against the Yingluck government," said Paul Chambers, director of research at the Institute of Southeast Asian Affairs at Chiang Mai University in northern Thailand.

He said Yingluck was likely to face increasing legal moves in connection with the failed Senate reform bill as well as allegations of corruption in her government's rice subsidy scheme.

"These decisions are going to be giving a lot of legitimacy to the demonstrators as they wreak havoc across Bangkok and parts of the south," Chambers said.

The civil strife is the worst since 2010, when more than 90 people were killed in street clashes between pro-Thaksin protesters and the military.

Thai stocks and the baht currency have fallen sharply on concerns that the latest turmoil will scare off tourists and investors.

Unless the crisis eases in the coming months, "we have to accept that the worst expectation will be that tourists drop about 50 percent," said Thanavath Phonvichai, economic forecaster at the University of the Thai Chamber of Commerce.

Singapore Airlines has already cancelled 19 flights to or from Bangkok up to late February, although the demonstrators have promised not to target the airports or public transportation.