Zimbabwean police plan to charge activist pastor Evan Mawarire with subverting the government, a crime which carries up to 20 years in jail on conviction, after violent protests this week left three dead and scores injured, a lawyers' group said.

Mawarire was arrested by armed police on Wednesday and initially charged with the lesser crime of inciting public violence after he circulated Facebook videos encouraging Zimbabweans to heed a stay-at-home strike called by the country's biggest labour union.

A doctors' group said on Thursday they had treated nearly 70 people for gunshot wounds while police rounded up hundreds after the protests, which were triggered by President Emmerson Mnangagwa's decision to steeply raise fuel prices.