Ohio officials are investigating a violent arrest in which an officer was videotaped repeatedly punching a black man, the latest alleged case of excessive use of force by police against African Americans.

By early Friday, more than seven million people had viewed an online video of the arrest, posted on Facebook by a bystander.

Police also released dashboard camera footage showing 25-year-old Richard Hubbard forced to the ground with an officer on top of him raining down blows.

In an initial report of the incident, which occurred last Saturday, police said Mr Hubbard had been resisting arrest. He can be seen apparently struggling with officers, but not exhibiting violent force.

City officials said the incident raised questions and they were investigating, while advocates representing residents of the small city of Euclid, a suburb outside Cleveland, expressed alarm.

"Violence and use of force in any situation is disturbing and difficult to watch," Euclid Mayor Kirsten Gail said in a statement.

Questions have arisen over the police department's hiring practices and how thoroughly it vets officers.

The officer who punched Mr Hubbard was not identified. But, the American Civil Liberties Union said one of the police at the scene was Michael Amiott, who was "forced to resign from his previous job" at another police department.

"We are appalled by the brutality seen in these videos," head of the Ohio chapter of the American Civil Liberties Union J. Bennett Guess said.

"This behaviour underscores a disturbing pattern of extreme use of force by police in our state and across our nation."

The incident was the latest to expose deep rifts between many African Americans and US police -- especially after recent high-profile incidents of police use of force captured on video.

Anger over police conduct and repeated failures to convict accused officers at trial has boiled over into angry street protests.

In Milwaukee, Wisconsin -- another US city with strained relations between police and African Americans -- violent protests erupted after a 23-year-old black man was shot by a black officer after a brief foot chase.