Hundreds of Bangladeshi opposition activists have been arrested, police and party officials said Friday, ahead of a major rally where campaigners hope more than a million people will take to the streets of Dhaka.

The Bangladesh Nationalist Party (BNP) and its leftist allies, along with several Islamist outfits, have been mounting protests demanding Prime Minister Sheikh Hasina quit and let a neutral government oversee elections due by the end of January.

Hasina -- daughter of the country's founding leader -- has been in power for 15 years and has overseen rapid economic growth with Bangladesh overtaking neighbouring India in GDP per capita, but her government is accused of corruption and human rights abuses.

The BNP has called a "grand rally" for Saturday, with party spokesman Zahir Uddin Swapan saying it expects "more than a million people" to turn out.

"A sea of people will join the protest," he told AFP.

He said police had arrested at least 1,500 people including several senior BNP officials in the past four days in an effort to disrupt preparations.

"They have raided door to door and arrested people while they were holding meeting indoors," he said.

Dhaka Metropolitan Police (DMP) spokesman Faruk Hossain confirmed there had been detentions but rejected the figure, saying some 400 BNP activists and supporters had been held in the past week.

"We are arresting only those people who face cases or arrest warrants," he told AFP.

Police have set up checkposts at entry points to the capital, Dhaka district police chief Mohammad Asaduzzaman told AFP, in what the opposition says is a tactic to prevent its activists entering the city.

Bangladesh's largest Islamist party, Jamaat-e-Islami, has also called a demonstration on Saturday, but DMP spokesman Faruk said authorities had banned the party from holding any protests.

"We'll defy the ban and hold our protests peacefully, holding protests is our constitutional right," said party spokesman Hamidur Rahman Azad, adding police had arrested more than 140 Jamaat activists over the past three days.

Western governments have expressed concern over the political climate in Bangladesh, where Hasina's ruling Awami League dominates the legislature and runs it virtually as a rubber stamp.

Her security forces are accused of detaining tens of thousands of opposition activists, killing hundreds in extrajudicial encounters and disappearing hundreds of leaders and supporters.

The elite Rapid Action Battalion (RAB) security force and seven of its senior officers were sanctioned by Washington in 2021 in response to those alleged rights abuses.

The BNP's ailing leader Khaleda Zia, a two-time premier and old foe of Hasina's, is effectively under house arrest after a conviction on graft charges.