WASHINGTON : A man was gravely wounded in a gun battle with police as street protests turned violent in Ferguson, Missouri, on Sunday night, capping a day of peaceful rallies to mark the fatal shooting of an unarmed black teenager by a white officer one year ago.

The unidentified man in his 20s was undergoing surgery early Monday. He unleashed a "remarkable amount of gunfire" against the officers using a stolen handgun, police said. Several volleys of gunshots rang out as police in riot gear tried to disperse demonstrators blocking traffic and smashing storefront windows along a street that was a flashpoint of last year's unrest. Police said gunfire began with two groups of agitators apparently shooting at each other before one gunman darted across a parking lot and was confronted by four officers who pulled up in an unmarked vehicle. An investigation is on.