A man accused of opening fire on a Fourth of July parade near Chicago has been charged with seven counts of murder, officials say.

Robert Crimo, 21, would be punished "for the killing spree he has unleashed against our community", Lake County State Attorney Eric Rinehart said.

The attack in Highland Park left seven dead and more than 30 others injured.

Mr Rinehart added that dozens more charges would be filed before the investigation was over.

"These are just the first of many charges that will be filed against Mr Crimo," he said to cheers and applause from the crowd gathered for the news conference on Tuesday. "I want to emphasise that. There will be more charges."

The suspect is accused of firing 70 bullets from a high-powered rifle down on to the crowd and disguising himself as a woman so he could escape alongside fleeing victims.