DHAKA, Bangladesh (AFP) — Tens of thousands of supporters of Bangladesh's main opposition party descended on Dhaka Saturday to protest against the government of Prime Minister Sheikh Hasina and demand new elections.

"Sheikh Hasina is a vote thief," they chanted at the Golapbagh sports ground where the rally was being held, as the crowd spilled over into the surrounding streets.

Tension was high in the capital after security forces stormed the headquarters of the opposition Bangladesh Nationalist Party on Tuesday, leaving at least one person dead and scores injured.

Two of the party's top leaders were arrested on Friday over charges of inciting the violence, adding to the 2,000-odd activists and supporters the party said had been detained since 30 November to try to prevent the rally from going ahead.

Western governments — along with the United Nations — have expressed concerns over the political climate in Bangladesh, one of the fastest-growing economies in Asia.

The country was long aligned with the United States but in recent years, Hasina has courted deeper ties with China, with Beijing bankrolling some of her multi-billion-dollar infrastructure projects.

The opposition has been holding protests around the country demanding Hasina resign and call an election under a caretaker government — which she has rejected outright.

A BNP official claimed that some 200,000 people had joined Saturday's rally by mid-morning.

"Our main demand is Sheikh Hasina resign and parliament is dissolved and let a neutral caretaker government step in to hold a free and fair election," spokesperson Zahiruddin Swapan told AFP.

Dhaka Metropolitan Police spokesperson Faruq Ahmed dismissed the figures, saying the venue could not hold more than 30,000 people.

There had been no violence so far, but SWAT teams, counter-terrorism units and canine squads were on standby, he added.

Police set up checkpoints on routes into the city and security was tight across the sprawling metropolis of some 20 million people.