Bangladesh's main opposition officially boycotted upcoming general elections Thursday, removing the only party that could have offered a realistic challenge to Prime Minister Sheikh Hasina's fourth consecutive term in power.

The Bangladesh Nationalist Party (BNP), warning that thousands of its members had been arrested in a sweeping crackdown, said it had not applied to contest a single seat on the last day of filing candidate nominations before the January 7 polls.

"We are boycotting the election," A.K.M Wahiduzzaman, a spokesman of the party, told AFP.

"We remained steadfast to our stand that we will not take part in any election with Sheikh Hasina in power".

The BNP and other parties have held mass protests calling on Hasina to quit power and let a neutral government run the polls, demands the government has said are unconstitutional.

Human Rights Watch warned Monday of a "violent autocratic crackdown", with almost 10,000 opposition activists arrested and at least 16 people killed since protests escalated in October, including two police officers.

Wahiduzzaman, accusing Hasina of having "rigged the previous two elections", said the number arrested was even higher.

"She has arrested more than 18,090 of our leaders and supporters in an unprecedented crackdown since late October 28 to rig another election," he said.

"We won't join any farcical election."

Hasina has overseen massive economic growth during her 15 years in power, but there has been international alarm over democratic backsliding and thousands of extrajudicial killings.

Other key opposition parties have also said they will boycott the elections, including the Jamaat-e-Islami, the country's largest Islamist party, and the Islami Andolon Bangladesh.

Election Commission spokesman Shariful Alam said they would confirm who was participating later Thursday.

Apart from the ruling Awami League, several smaller allied parties have said they will take part.

Some BNP officials are understood to have left the party hoping to contest a seat as independents.