Clashes between supporters of the ruling party and opposition and the use of force by the police resulted in the deaths of at least 18 people on election day.
At least 18 people were killed in election-day clashes in Bangladesh on Sunday, the ruling party said in a post-election briefing.
Parliamentary polls came to a close, following a bloody campaign period overshadowed by a crackdown on the opposition by Prime Minister Sheikh Hasina, who is expected to win a historic but controversial fourth term.
Voting was held under tight security until 1000 GMT (4:00 pm) in a parliamentary election that is expected to deliver a historic but tainted fourth victory for Hasina.
More than 40 candidates of the opposition alliance pulled out during polling alleging vote rigging, local media said.
Nearly 287 candidates had contested the election from the opposition group led by the Bangladesh Nationalist Party.
Bangladesh's Election Commission told Reuters it was investigating allegations of vote rigging coming from across the country.
A source in the opposition said many candidates pulled out individually but that the group's final decision would be announced later in the day.
Vote counting has already begun and results are expected to be clear by Monday morning.
Deaths on Election Day
At least three men were shot by police while eight others died in clashes between activists from the ruling Awami League Party and opposition Bangladesh Nationalist Party (BNP), police said.
An auxiliary police member was killed after being attacked by opposition activists armed with guns and sticks, according to officials.
Police said they acted "in self-defence" in the southern town of Bashkhali, when they opened fire on opposition supporters who had attempted to storm a polling booth, killing one.
In a separate incident, another man was shot by police after he tried to steal a ballot box.
TRT World's Shamim Chowdhury reports from Dhaka.
Pre-poll crackdown and violence
Bangladesh's leader has been lauded for boosting economic growth in the poor Asian nation during an unbroken decade in power and for welcoming Rohingya refugees fleeing a military crackdown in neighbouring Myanmar.
But critics accuse her of growing authoritarianism and crippling the opposition – including arch-rival Khaleda Zia who is serving 17 years in prison on graft charges she says are politically motivated – in a bid to cling on to power.
The weeks-long election campaign was marred by violence between supporters of Hasina's Awami League and activists from the BNP, led by Zia.
Free and fair?
Opinion polls following the crackdown show Hasina, who has presided over six percent GDP expansion every year since she won a landslide in 2008, heading for a comfortable victory that would extend her reign as the country's longest-serving leader.
She needs 151 seats in the first-past-the-post system to win in the 300-seat parliament but experts say any victory would be sullied by accusations that she hamstrung her opponents' campaign and scared people into voting for her.
The opposition says more than 15,000 of its activists have been detained during the weeks-long campaign, crushing its ability to mobilise its grassroots support.
"We are getting disturbing reports outside Dhaka that overnight votes have been cast illegally," said Kamal Hossain, the 82-year-old architect of Bangladesh's constitution who is helming the opposition coalition.
Presiding officers at polling stations across Dhaka reported a low turnout in morning voting.
Human Rights Watch and other international groups have decried the crackdown, saying it has created a climate of fear which could prevent supporters of opposition parties from casting their ballots.
The United States has also raised concerns about the credibility of the Muslim-majority country's election while the United Nations called for greater efforts to make the vote fair.
Seventeen opposition candidates have been arrested over what they claim are trumped-up charges while another 17 were disqualified from running by courts which Hasina's opponents say she controls.
"This is not (a) free and fair election. It is more a controlled selection," said a Western diplomat who asked not to be named.