Voting began Sunday in Bangladesh's contentious parliamentary elections, seen as a referendum on what critics call Prime Minister Sheikh Hasina's increasingly authoritarian rule.

Hasina's main rival is former Prime Minister Khaleda Zia, the leader of the opposition Bangladesh Nationalist Party, deemed ineligible by a court from running for office because she is in prison for corruption.

The two women have been in and out of power — and prison — for decades.

In Zia's absence, opposition parties have formed a coalition led by Kamal Hossain, an 82-year-old Oxford-educated lawyer and former member of Hasina's Awami League party.

By 8 a.m. Sunday when polls opened, about 80 people had lined up to cast their ballot at a voting center in Dhaka's Uttara Model Town area.

Polling workers appointed by candidates showed Election Commission officials empty ballot boxes before the first paper ballot was cast.

Awami League supporters had set up help desks on the street outside the polling station for voters to find their registration serial numbers.

Ashraful Islam, a retired engineer, was among the first in line at the Uttara Model Town voting center.

"I am very happy," he said.

The election campaign has been marred by the arrests and jailing of what the opposition says are thousands of Hasina opponents, including six candidates for Parliament. At least a dozen people were killed in campaign-related clashes.

"Hasina's use of the state machinery to subjugate the opposition virtually ensures her electoral victory," said Sasha Riser-Kositsky, a South Asia analyst for New York-based Eurasia Group.

Both sides are hoping to avoid a repeat of 2014, when Zia and the BNP boycotted elections and voter turnout in the South Asian nation of 160 million people was only 22 percent. More than half of the 300 parliamentary seats were uncontested. The Awami League's landslide victory was met by violence that left at least 22 people dead.

This election, some 104 million people are eligible to vote, including many young, first-time voters.

While rights groups sound the alarms about the erosion of Bangladesh's democracy, Hasina has promoted a different narrative, highlighting an ambitious economic agenda that has propelled Bangladesh past larger neighbors Pakistan and India by some development measures.

Voting is expected to conclude at 4 p.m. across more than 40,000 polling stations. Counting will begin soon after the voting ends. Hasina, who is seeking a third consecutive term, cast her ballot in Dhaka.

About 600,000 security officials, including army and paramilitary forces, have been deployed across the country in a bid to contain violence in Bangladesh's 11th general elections. Bangladesh's telecommunications regulator shut down mobile internet services nationwide to prevent possible protests from organizing.