Dozens were injured on Sunday as Bangladeshi police fired rubber bullets and tear gas at opposition activists to prevent new protests over the death of a writer in jail, police and a party official said.

Live footage from local television station Channel 24 showed a road and footpath in front of the National Press Club -- a favourite protest site in the capital Dhaka -- turning into a battleground as police beat protesters with batons to disperse them.

Clashes ensued as student activists from the main opposition Bangladesh Nationalist Party (BNP) hurled rocks and attacked officers with plastic pipes, prompting police to retaliate by "firing rubber bullets and tear gas", Deputy Commissioner of Dhaka police Sazzadur Rahman told AFP.

"They did not take any permission (for the protests)," he added, defending the police's move to clear the protesters.

BNP spokesman Rizvi Ahmed said about 30 student activists of the party including a senior leader were injured in the clashes. Several policemen were also hurt, including an officer who was rushed to hospital. 

He said more than 500 protesters were at the press club, trying to form a human chain to protest the death of writer Mushtaq Ahmed, who collapsed in a high-security prison north of Dhaka and died late Thursday.

He defended the party not having sought permission for the protests at the National Press Club, saying that historically no clearance was needed to hold any rallies there.

"As they stood there for a human chain, (police) baton-charged indiscriminately," he said.

"It is a murder," he said of Mushtaq Ahmed's death. "We think the state is involved."

International and local rights groups have demanded a swift probe into the death of the writer 10 months after he was arrested over comments posted on social media.

Ambassadors from 13 countries, including the United States, France, Britain, Canada and Germany, expressed "grave concern" over the case.

He had been detained under the controversial digital security laws that critics say are used to muzzle dissent.

Ahmed was denied bail at least six times.

Bangladesh Prime Minister Sheikh Hasina on Saturday shrugged off criticism of her government's rights record, international concern over the internet law and Ahmed's death.

Demonstrators have marched at Dhaka University over the last few days chanting slogans condemning the government's treatment of Mushtaq Ahmed as well as other writers, journalists and activists.