The violence broke out after a man refused to accept a fine for parking in the wrong location, the Georgia-based Democracy & Freedom Watch website reported.
The man argued with police and was detained, the report said.
The website showed video of hundreds of protesters throwing stones in the darkness of the Batumi streets.
Zaal Mikeladze, the regional medical minister, told reporters that 11 police officers and 10 demonstrators were hospitalized with injuries and from the effects of tear gas.
Several people were arrested, but Georgian Interior Minister Giorgi Mgebrishvili said he ordered those arrested to be released in an effort to calm tensions.
The Rustavi-2 TV network reported some protesters tried to storm a police station and set fire to police cars.
Batumi is the country's second-largest city and a popular tourist destination.
Media reports quoted opposition politicians as saying the public in Batumi had been angered by what they see as disproportionately high fines by police for minor traffic offenses.
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