Prime Minister Sheikh Hasina cast her vote on Sunday soon after polls opened in a general election in Bangladesh that is set to carry her Awami League-led alliance to a fourth straight term amid a boycott by the main opposition party.

Accompanied by her daughter and other members of her family, Hasina voted at City College in the capital, Dhaka, minutes after polling began at 8 am. It will run until 4 pm, followed by the counting of votes.

Initial results are expected early on Monday, though Reuters witnesses said voter turnout was low in the chill and fog of a winter morning preceded by violence in the run-up to the election.

"Bangladesh is a sovereign country and people are my power," Hasina said after voting, adding that she hoped her party would win the people's mandate, which would give it a fifth term.

At least four people were killed on Saturday in a passenger train fire that the government called arson after several polling booths, schools and a Buddhist monastery were set ablaze last week.

There were no reports of violence on voting day, however, as nearly 800,000 security forces guard polling booths, assisted by troops nationwide.

Rights groups have warned the country of 170 million is headed for virtual one-party rule after the boycott by the Bangladesh Nationalist Party (BNP) and some smaller allies.

The United States and Western nations, key customers of its garment industry, have called for a free and fair election - the 12th since independence from Pakistan in 1971.Hasina said she did not need to prove the credibility of the election to anyone. "I have to answer to the people of Bangladesh," she said.

"What is important is if the people of Bangladesh will accept this election."

About 120 million voters will choose from nearly 2,000 candidates for 300 directly elected parliamentary seats. There are 436 independent candidates, the most since 2001.

The BNP says the Awami League has propped up "dummy" candidates as independents to try to make the election look credible, a claim the ruling party denies.

The BNP, which also boycotted the 2014 poll though it took part in 2018, has asked people to shun Sunday's election and called a two-day strike nationwide from Saturday.

Hasina, who refused BNP demands to resign and cede power to a neutral authority to run the election, accuses the opposition of instigating anti-government protests that have rocked Dhaka since late October and killed at least 14 people.

In her last 15 years in power, Hasina, 76, has been credited with turning around Bangladesh's economy and the garment industry.

But critics have also accused her of authoritarianism, human rights violations, crackdowns on free speech and suppression of dissent.

The economy has slowed sharply since the Russia-Ukraine war pushed up prices of fuel and food imports, forcing Bangladesh to turn last year to the International Monetary Fund for a bailout of $4.7 billion.