Voters in Bangladesh began casting their ballots as polls opened in an election fraught with violence and a boycott from the main opposition party, paving the way for prime minister Sheikh Hasina and her Awami League to seize a fourth consecutive term.

Authorities said at least 18 arson attacks were reported across the country since late Friday, with 10 of them targeting polling places.

Four people died Friday in an arson attack on a passenger train heading toward the capital, Dhaka.

The incidents have intensified tensions ahead of the parliamentary elections that the opposition Bangladesh Nationalist Party and its allied groups said they would shun.

Campaigning in the South Asian nation of 169 million has been marred with violence as at least 15 people have been killed in recent months.

Hostilities reached a boiling point in late October, after a massive rally in Dhaka by the BNP saw clashes with police.

As the election neared, authorities blamed much of the violence on the BNP, who they accuse of seeking to sabotage the election.

On Saturday, detectives arrested seven men belonging to the BNP and its youth wing for their alleged involvement in the passenger train attack.

The opposition party denied any role in the incident, and say they are being blamed by authorities who want to discredit their “peaceful and nonviolent movement”.

On Sunday morning, Ms Hasina and her daughter voted amid tight security at Dhaka City College, as other citizens lined up outside to cast their ballot.

The 76-year-old Ms Hasina, the country’s longest-serving leader and one of its most consequential, is widely expected to be re-elected for a fifth overall term.

But a victory would come with a deeply contentious political landscape.

The vote, like previous elections, has been defined by the bitter rivalry between Ms Hasina’s Awami League and BNP, led by former premier Khaleda Zia, who is ailing and under house arrest on corruption charges.

The two women ran the country alternatively for many years, cementing a feud that has since polarised the country’s politics and fuelled violence around elections.

It has also stoked questions over whether the polls are credible, if there are no major challengers to take on the incumbent.

Critics and rights groups say the vote follows a troubling pattern, where the past two elections held under Hasina were marred by allegations of vote-rigging, which authorities have denied, and another boycott by opposition parties.

The government has rejected a monthslong demand by the BNP to have a neutral caretaker government administer Sunday’s vote.

Instead, the government has defended the election, saying 27 parties and 404 independent candidates are participating.

But with scores of those independent candidates from the Awami League itself, and mostly smaller opposition parties in the race, analysts say the result is near inevitable.

Michael Kugelman, director of the South Asia Institute at the Wilson Centre, said none of those contesting would be able to mount much of a challenge to Ms Hasina’s party, saying “the outcome is all but guaranteed, and that is that the Awami League will return again”.

“This suggests that Bangladesh’s democracy will be in an extremely precarious state once the election is done,” he added.

The vote has also been called into question by accusations of a sweeping crackdown against the BNP.

The party says thousands of their members were rounded up and jailed ahead of the vote on trumped-up charges, but the government disputed the figures and denied that arrests were made due to political leanings.

Ms Hasina is credited with transforming the economy in a young nation born out of war, and making its garment sector one of the world’s most competitive.

Her supporters say she has staved off military coups and neutralised the threat of Islamist militancy.

And internationally, she has helped raise Bangladesh’s profile as a nation capable of doing business and maintaining diplomatic ties with countries often at odds with each other, like India and China.

Yet her critics say her rise has risked turning Bangladesh into becoming a one-party state where democracy is under threat, as emboldened government agencies increasingly use oppressive tools to mute critics, shrink press freedoms and restrict civil society.

The global economic slowdown is also being felt in Bangladesh, exposing cracks in its economy that have triggered labour unrest and dissatisfaction with the government.

In the capital, posters of Awami League candidates and the party’s boat symbol are ubiquitous, with images of Ms Hasina plastered on numerous banners dotting the city.

After casting her ballot, Ms Hasina dismissed concerns over the legitimacy of the vote.

“I have my accountability to people. … Whether they have accepted this election or not, that is important to me,” she told reporters.

“I’m trying my best to ensure that democracy should continue in this country,” Ms Hasina added.

“Without democracy, you cannot make any development.”

Polls were to be open for eight hours across the country for some 119 million eligible citizens to vote in over 42,000 stations.

Polling will be held in 299 constituencies out of 300, as the election in one constituency was postponed after an independent candidate died of natural causes.

About 700,000 security officials have been deployed to guard the polls and more than 120 foreign observers have arrived to monitor the vote, according to the Election Commission.