SYDNEY - A man has been arrested over an alleged double shooting at Merrylands in Sydney's west overnight, police said Thursday.

Police arrested the 27-year-old man in a raid at a house in Lansdowne Street in Merrylands on Thursday morning and are still hunting for three others linked to an armed robbery.

Police said one of the victims, a 62-year-old man, was shot in the chest after going to investigate a fight outside his home on Lansdowne Street in Merrylands.

Another 19-year-old man was shot several times in the chest, stomach and arm.

Both injured men were taken to Westmead Hospital, with the younger man in a stable condition and the older one remaining in a critical condition.

Police have been told that at around 10:50 pm(local time) on Wednesday, the 19-year-old man drove to Lansdowne Street with two others, aged 17 and 18, to purchase a mobile phone advertised on a social networking website.

Upon reaching Lansdowne Street they were flagged down by two men and one got into the backseat of the vehicle, allegedly armed with a handgun.

He allegedly demanded money and personal belongings while two more men approached the car.

The 19-year-old was shot several times following an altercation within the vehicle.

The gunman ran down street with his three accomplices after the shooting.