BANGKOK - Thailand is holding elections on Sunday in five provinces where voting was disrupted in last month's poll by anti-government protesters trying to unseat Prime Minister Yingluck Shinawatra.

Election re-runs planned for April in other provinces have been suspended pending a court decision on procedures.

Voting was disrupted in 18 percent of constituencies, 69 out of 375, nationwide, the Election Commission said, affecting 18 of 77 provinces.

The demonstrators, who have blocked intersections in the capital for weeks, say Yingluck must resign and make way for an appointed "people's council" to overhaul a political system they say has been taken hostage by her billionaire brother and former premier, Thaksin Shinawatra.

The election is almost certain to return Yingluck to power, thanks to her support base in the largely rural north and northeast, a result the opposition will never accept.

The result cannot change the dysfunctional status quo in a country popular among tourists and investors yet blighted by eight years of polarisation and turmoil, pitting the Bangkok-based middle class and royalist establishment against the mostly poor, rural supporters of the Shinawatra family.

Protest leader Suthep Thaugsuban's supporters were due to abandon their protest sites on Sunday and move to central Lumpini Park, where many protesters already sleep in tents near an established protest stage on the edge of the Silom financial district.

"For those who worried that I may give up, I can reassure that an old man like me does not know how to give up," Suthep said on Saturday, in reference to the scaled-down protest.

"That's because there are millions of people who support me ... This is not a move to retreat, but it is an adjustment in our manoeuvre for fighting," he said.

Protest numbers have dwindled amid attacks on various camps with grenades and guns. Three people were killed when a grenade was thrown into a busy shopping area near one camp last Sunday.

In total, 20 people have been killed in protest-related violence in Bangkok since November 30 and three in the eastern province of Trat.