Several of Zimbabwe's main trade union leaders, who were arrested after Wednesday's banned protests, have been transferred from prison to hospital.
Wellington Chibebe was being held in a Harare police station
Lawyer Alec Muchadehama, representing the unionists, said that 12 people were now in hospital having been badly beaten while in police custody.
Police spokesman Wayne Bvudzijena said they were aware of the allegations and investigations were underway.
He added that "excessive" attitudes within the force were not condoned.
At least 50 people were arrested on Wednesday while trying to stage demonstrations to protest against the government's handling of Zimbabwe's economic crisis.
The government had said the protests were banned.
Zimbabwe's main trade union leader, Wellington Chibebe, was one of those arrested.
His lawyer said he was badly beaten by the police.
"Chibebe has two fractures on the left arm, cuts on his head and bruises on his body," said Mr Muchadehama.
Police spokesman Wayne Bvudzijena confirmed that Mr Chibebe was in hospital but denied that the police routinely beat protesters.
"As an organisation we don't have a culture of assaulting people in our custody.
"Conduct of police officers can vary from time to time but we have principles that an officer has to follow."
The British government condemned the crackdown, describing it as a further abuse of human rights and has urged the country's government to begin a process of national dialogue and undertake a reform programme based on national consensus.
Zimbabwe's economy has been in sharp decline for more than six years.
President Robert Mugabe blames the problems on a foreign plot to remove him from power.
His critics say his policies have ruined what used to be one of Africa's most developed economies.