Police fired tear gas and rubber bullets at huge crowds of Bangladesh opposition supporters on Saturday to break up a giant protest against the prime minister, with an officer and a protester killed in several hours of violent clashes in central Dhaka.

More than 100,000 supporters of two major Bangladesh opposition parties rallied to demand Prime Minister Sheikh Hasina step down to allow a free and fair vote under a neutral government.

Live footage on the verified Facebook page of the main opposition Bangladesh Nationalist Party (BNP) showed thousands of people running for safety as sound grenades went off one after another and plumes of black smoke rose from the roads.

Witnesses said the violence spread in roads and alleys in the centre of the capital as police fired tear gas and rubber shotgun rounds, while the protesters threw stones and bricks.

One officer was killed and more than 100 injured, said Dhaka Metropolitan Police spokesman Faruk Hossain, saying: "The constable was hacked in the head by opposition activists."

BNP said one of its youth wing activists was killed during Saturday's clashes.

"Shamim Molla, one of our youth wing leaders, was shot dead by police. His body is at a hospital at Rajarbagh (in central Dhaka)," said Sayrul Kabir Khan, a spokesman of the party.

The protests by the BNP and the largest Islamist party, Jamaat-e-Islami, were the biggest so far this year, and marked a new phase in their protests with a general election due within three months.

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 inflation has risen and her government is accused of corruption and human rights abuses.

At least 20 people were rushed to Dhaka Medical College Hospital, the country's largest, with wounds from rubber bullets, police inspector Bacchu Mia said.

The clashes began in front of the city's largest Catholic church when rowdy opposition supporters fought with sticks and allegedly torched a bus and a police post.

Both BNP and Jamaat-e-Islami called for a nationwide strike on Sunday to protest the violence. (AFP)