COLOMBO: Sri Lanka went to the polls Thursday in its tightest election in decades, with its strongman president battling for survival after accusations of corruption and a failure to bring about national reconciliation.

Mahinda Rajapaksa appeared assured of victory when he called snap polls in November, seeking an unprecedented third term in office five years after crushing a violent separatist rebellion that had traumatised the country for decades.

Rajapaksa, 69, came to power in 2005 and won a second six-year term in 2010 on a wave of popularity after the military defeated Tamil Tiger separatists, ending a 26-year civil war.

But his health minister's shock decision to defect from the government and stand against him led to a bitterly fought campaign for an election analysts say is too close to call.

Maithripala Sirisena was a relative unknown until he announced he was standing as the main opposition candidate, but has led a slew of defections and become a rallying point for disaffection with Rajapaksa and his powerful family.

Casting his ballot in his southern constituency of Hambantota, Rajapaksa said he was confident of re-election. “We will have a resounding victory. That is very clear,” he said.

With independent monitors warning of voter intimidation, particularly in the Tamil-dominated north of the country, Washington urged Rajapaksa to ensure the election was peaceful and credible.

Top US diplomat John Kerry spoke with the president to underscore the government's responsibility to ensure the polls were “free from violence and intimidation,” State Department spokeswoman Jen Psaki said.

Opposition supporters have accused the government of deploying troops to Tamil areas to intimidate voters.

Rajapaksa is widely detested by members of the country's biggest minority, who account for 13 per cent of its 15 million people.

South Asia's longest-serving leader had appeared politically invincible after his forces crushed the Tamil Tigers in 2009 and brought peace to the island.

He won a landslide election victory in 2010, but critics say he has failed to bring about reconciliation with Sri Lanka's Tamil minority in the years that followed.

His second term has been dogged by accusations of corruption, including undermining the independence of the judiciary and lining the pockets of political cronies through lucrative contracts.

Sirisena promised a new political culture as he cast his vote in the eastern town of Polonnaruwa. “My victory is in sight. There is support for us everywhere. From tomorrow, we will usher in a new political culture,” he said.

Growing authoritarianism

With turnout expected to be high, large queues were seen outside polling stations. Voting will continue for nine hours under tight security, with results expected on Friday. There are 19 candidates in all.

The 69-year-old president, who has been accused of growing authoritarianism, removed the two-term limit on the presidency and gave himself more powers soon after winning his second term.

He has packed the government with relatives, sparking resentment even within his own party.

Opposition parties including the main Tamil party have rallied behind Sirisena, the 63-year-old farmer-turned-politician, who, like Rajapaksa, is from the majority Sinhalese community.

“Sirisena has become the symbol for those arguing for better governance in this country and anti-corruption,” said Paikiasothy Saravanamuttu, director of the Centre for Policy Alternatives think tank.

The president has taken drastic measures to shore up support, slashing fuel prices, cutting water and electricity tariffs and giving subsidised motorcycles and hefty pay increases to 1.6 million public servants.

Sri Lanka's economy has grown by an annual average of over seven per cent since the war ended, partly thanks to hefty investment from China.

But the opposition says Chinese contractors have employed few local people, and household incomes have not kept pace with national growth rates.

Sri Lanka is a mainly Buddhist country, but has sizeable Hindu, Muslim and Christian minorities.

The independent Centre for Monitoring Election Violence (CMEV) said this week it had documented 420 incidences of violence during the campaign, with the north worst hit. .