Bangladeshi courts have convicted more than 200 officials and activists of the main opposition Bangladesh Nationalist Party, mostly in absentia, lawyers said on Thursday, taking the number sentenced since last month to nearly 500.

The BNP said the cases were politically motivated, aimed at crushing the only opposition party in the country that can offer a realistic challenge to Prime Minister Sheikh Hasina's 15-year rule.

Bangladesh holds a general election on January 7, with Hasina eyeing her fourth consecutive term in power.

Many were convicted on historic charges over protest violence, with sentences ranging from 2.5 to seven years.

Monir uz Zaman, a prosecutor, said 75 BNP activists were sentenced in a Dhaka court to 2.5 years on charges of violence and arson during political turmoil in 2013.

Zaman said 72 of the 75 were "absconding" and were now wanted fugitives.

Atauar Rahman, a prosecutor at the Dhaka Metropolitan Magistrate court, said that 112 BNP activists were convicted in two separate cases of violence in 2013 and 2018.

Taposh Kumar Paul, another prosecutor, said another Dhaka court sentenced 12 BNP activists to seven years in jail for violence in 2015.

Nazrul Islam, a defence lawyer, said 11 more BNP members were sentenced to seven years in jail on Wednesday for violence during political clashes in 2013.

Several of those convicts were also sentenced in absentia.

Islam said cases had been "conducted in a hurry."

Kayser Kamal, BNP's legal chief, said nearly 500 BNP senior officials and activists have been sentenced in recent days.

They included former lawmakers, youth and student leaders and those who had hoped to contest elections.

"These cases are staged, baseless and politically motivated," he said. "Trials of these cases started all of a sudden just a few weeks before the national election."

The BNP has staged a series of major rallies and marches in a bid to force Hasina to quit power and let a neutral government run the polls.

But since late last month, the police have cracked down on the opposition, arresting almost the entire top leadership of the BNP and arresting thousands of its activists and supporters.

Hasina has overseen impressive economic growth during her 15 years in power, but there has been international alarm over her increasingly authoritarian rule and thousands of extrajudicial killings.

Amnesty International has raised concerns over the convictions, saying they are part of a pre-election repression of the opposition.

"It is important to note that those incarcerated are not allowed to vote in Bangladesh," said Yasasmin Kaviratne, a South Asia regional campaigner of Amnesty International.

Amnesty International has documented "a chilling pattern of repression in Bangladesh where opposition leaders and activists have been repeatedly arbitrarily arrested solely for their dissenting views, especially a few weeks ahead of the election," she added.

Apart from the convictions, the BNP and the Jamaat-e-Islami, the country's largest Islamist party, said at least 16,000 of their activists have been arrested since October 28 when police broke up a major opposition rally in Dhaka after the killing of an officer in clashes.

Police haven't disclosed the full figure of the arrests but said those who were arrested had warrants against their names.

In a statement police have also accused opposition members of torching nearly 290 vehicles, mostly buses, during their more than three weeks long nationwide strikes and transport blockades.

At least six people were killed in the violence, police said. (AFP)