Motorcycle gang members and convicted criminals barred from buying guns in South Australia have no difficulty obtaining illegal firearms - including fully automatic weapons.

These are often used in drive-by shootings, robberies and murders.

Police seized a Soviet-made SKS semi-automatic rifle, a sawn-off .22 calibre rifle and an illegal silencer in raids on 11 suburban properties belonging to people associated with the Finks outlaw motorcycle club. Five people arrested in the Monday-night raids were charged with firearms and drugs offences.

The arrests and seizure of guns came a day after feuding Comancheros Motorcycle Club members were involved in a gunfight outside the Caffe Paesano, shooting at each other with what police suspect were illegal handguns.

The bikies' dispute outside the popular North Adelaide cafe spilled on to busy O'Connell St, forcing patrons to duck for cover.

Speculation linking the Hells Angels - bitter rivals of the Comancheros - to the gunfight was without foundation.

Police released security photos of a man wanted for questioning.

However, they would not confirm if he was the man who fired the first shot or one of three Comancheros who were seated at an outside table.

Police Assistant Commissioner Grant Stevens said illegal firearms were a recurring problem.

"We have seized automatic firearms ... rifles, semi-automatics, fully automatic weapons, shotguns, cut-down firearms," he said. "There are a lot out there and, as quickly as we take them out, (criminals) are sourcing other illegal firearms."

Latest police figures show offences with firearms and other weapons increased from 3557 to 3891 in the 2010-11 financial year.

The Crime Gangs Task Force has seized more than 235 illegal firearms since it was formed about four years ago but the flow of illegal weapons continues via corrupt dealers and gun manufacturers or thefts from private homes, gunshops and even armouries.

Without proper controls at state borders, weapons stolen or manufactured interstate can easily come into South Australia, Mr Stevens said.

Adelaide University Law School lecturer Allan Perry said there could be hundreds of thousands of illegal guns circulating in the country.

"Research indicates there are about 250,000 illegal firearms nationwide; it is a very substantial problem," he said.