Police in Greece have arrested an 89-year-old man following a double shooting which left five people injured.

The attacker initially opened fire at a social security agency in the Kerameikos area of Athens on Tuesday, wounding an employee in the leg, police say.

He then travelled to a courthouse around 5km (3.1 miles) away in Ambelokipi, where a further four people were reportedly injured, before fleeing the scene and leaving behind a shotgun, authorities add.

There is a heavy police presence at both locations and the motive for the shooting is not yet clear.

Police arrested the man at a hotel near the bus station in the port city of Patras, some 200km from the capital.

He was carrying a second weapon, a loaded .38 calibre revolver.

According to local media reports, the attacker had entered the buildings in Athens with a shotgun concealed under his coat.

ERT showed surveillance footage of the suspect calmly leaving the building on foot - with police investigating the possibility he had caught a taxi to the second location.

"I saw the whole thing... he was firing at the ground," one eyewitness told state news agency AMNA.

"Four women working at the small claims court were slightly injured," the head of the judiciary employees' union in Athens, Stratis Dounias, told the broadcaster.

The suspect's niece contacted authorities after recognising him as the man involved, state broadcaster ERT reports.

The five people - a man and four women - were left with non-life-threatening injuries in the shootings.

Gun violence in Greece is relatively uncommon, as firearm ownership is allowed but heavily regulated.