Thais voted Sunday to elect the upper house of parliament in a poll that could hold the key to the fate of the prime minister, who faces possible impeachment for negligence after months of street protests.
While the Senate is officially non-partisan, in reality the two main political camps are vying for control of the chamber in the absence of a functioning lower house following incomplete February polls.
Prime Minister Yingluck Shinawatra has resisted massive pressure to step down despite months of street protests and a slew of legal moves against her -- including over her alleged role in a rice subsidy scheme that could lead to an impeachment vote in the Senate.
Approximate turnout was around 40 percent representing nearly 19 million voters, the Election Commission said late Sunday.
There was also no repeat of the widespread disruption caused by anti-government protesters to a February 2 general election, which was boycotted by the main opposition party.
That vote was voided by the Constitutional Court earlier this month.
"Today's (Sunday's) election went smoothly... if the parties concerned create a stable political situation then an election can be successful," Election Commissioner Somchai Srisutthiyakorn told reporters.
With Thailand's political crisis lurching towards its sixth month, the Senate polls have taken on fresh importance.
Experts say the elected portion -- a narrow majority of the 150-seat chamber -- could install many pro-government senators to help bolster the administration in the face of looming legal challenges.
The other, unelected senators are appointed by institutions seen as allied to the anti-government establishment, such as the Constitutional Court and the Election Commission.
Preliminary results are expected Monday and the official list of newly elected senators could take days to approve.
But as senators do not formally represent political parties it was not immediately clear how the vote would affect the balance of power in parliament.
However, some candidates have had ringside seats during Thailand's recent political drama, which was sparked by the military coup that toppled wildly divisive billionaire Thaksin Shinawatra -- Yingluck's brother -- as premier in 2006.
An unofficial count said a former ombudsman and vocal Thaksin critic had swept the Bangkok senate vote, while the wife of a leading pro-government "Red Shirt" leader appeared to have won a landslide in a Shinawatra-allied stronghold of Udon Thani in the rural northeast.
Thaksin fled overseas in 2008 to avoid jail for a corruption conviction, but he is seen as the de facto leader of his sister's Puea Thai party and is reviled by the anti-government movement who accuse him of fostering corruption.
Yingluck has faced months of mass rallies demanding she step down to make way for an unelected interim government to oversee reforms aimed at rooting out the influence of the Shinawatra clan.
Political violence, often targeting protesters, has left 23 people dead and hundreds wounded in grenade attacks and shootings, although the bloodshed has abated since the demonstrations were scaled back at the start of March.
Observers say the crisis now appears to be entering a crucial new phase.
Yingluck has been summoned to appear before the National Anti-Corruption Commission (NACC) by Monday to defend herself against negligence charges linked to the rice scheme -- although it was unclear if she will attend in person.
The anti-graft body says she ignored warnings of corruption and financial losses in the flagship policy.
If indicted she would face an impeachment vote in the upper house that could result in her removal from office and a five-year ban from politics.
"The Senate could actually begin to hasten the end of the Yingluck government within two weeks of the NACC decisions on whether to impeach," according to Paul Chambers, director of research at the Institute of South East Asian Affairs at Chiang Mai University.
"That being said, if the elected senators are mostly pro-Thaksin, and they likely will be, then this development may sustain the Yingluck government," he added.
Her supporters have warned they will not tolerate the dismissal of another democratically elected government, raising the spectre of more turmoil on the streets.
The pro-Thaksin "Red Shirts" are preparing to stage their own mass rally on April 5 in a show of support for the government.
Their street rallies against the previous government in 2010 resulted in street clashes and a military crackdown that left dozens dead.