CHICAGO (AFP) - At least nine people were murdered in Chicago over the Independence Day weekend in an explosion of violence branded "simply unacceptable" by its mayor.

There were 50 shootings from suppertime Thursday through midnight Sunday in the third most populous city in the United States, a police spokesman said.

The Chicago Tribune gave an even higher toll, saying 82 people were shot, 14 fatally, over the Independence Day holiday - including a 13-hour stretch from Sunday afternoon in which four people were killed and 26 wounded.

It also reported that police had shot five people, including two teenagers who died after allegedly failing to obey an order to drop their weapons.

"The number of shootings and murders that took place over the holiday weekend is simply unacceptable," said Mayor Rahm Emanuel, a former chief of staff to President Barack Obama.

He appealed for a greater community effort to "give our young people alternatives to the street," on top of an effort to find ways to deploy more police officers.

Chicago saw 415 murders last year, more than any other major American city.