Protesters turned back drivers and blocked buses from carrying passengers in Zimbabwe's two main cities of Harare and Bulawayo. An AFP journalist saw protesters looting a supermarket.
The Zimbabwe Association of Doctors for Human Rights said it had "received widespread reports of protesters who have sustained gunshot wounds after being shot during the ongoing nationwide protests".
Thirteen cases had been reported by midday in and around Harare, it said in its statement. The extent of the injuries were still being assessed, it added.
Residents in Bulawayo said police fired teargas "indiscriminately" along city centre streets and into some residential areas. Bulawayo, Zimbabwe's second city, is seen as an opposition stronghold. Shops and banks pulled down their shutters in downtown Harare as riot police patrolled the streets and a military helicopter flew over the capital.
President Emmerson Mnangagwa on Saturday night announced a more than 100-percent rise in the price of petrol and diesel in a bid to improve supplies as the country battles its worst gasoline shortages in a decade.
Among the protesters at the Bulawayo demonstration was the celebrated writer Philani Nyoni.
"We have suffered enough," he told AFP, describing the government's decision as "stupid".