UPDATE: Second man arrested after Adelaide siege, shoot out

South Australian police have arrested a man, while a second remains in hospital with gunshot wounds, after a stand-off with tactical police in the Adelaide CBD today.

The second alleged offender was caught by heavily-armed officers a short time ago.

Police confirmed he was arrested without incident.

The incident was sparked about 5am after police were allegedly alerted to two men breaking into a business on East Terrace. The pair had apparently climbed onto the roof when they were confronted by police.

During the stand-off several shots were heard and police later confirmed they had opened fire and struck one man.

He was taken to hospital with non-life threatening injuries.

The stand-off continued for much of the day before police expanded their search for the second man about 4pm.

Several other buildings were reportedly searched.

Earlier, witnesses described the dramatic incident, saying one of the alleged offenders had been shot in the upper arm.

Footage of the incident suggests the man was warned repeatedly before being shot, with loud voices heard instructing him to "put it down" before the second gunshot is heard.