TEHRAN, Young Journalists Club (YJC) - The two men and two women, aged 50-72, were shot in the head and arm and all sent to a hospital, where two were in critical condition, Chief Inspector Hui Hong-kit told reporters.
A 44-year-old woman in possession of a gun was apprehended shortly afterward in a nearby shopping mall and was uninjured, Hui said.
"We believe the motive behind the attack was family conflict," he said, adding that police would also investigate how the suspect obtained the weapon.
Firearms are tightly controlled in Hong Kong and such shootings are highly unusual, usually restricted to armed robbers and members of organized crime groups known as triads.
The Asian financial hub is considered generally safe, although thieves this year have twice attacked jewelry stores using hammers.
According to police statistics, 10 murders were recorded between January and April this year, up by two from the same period last year. It wasn't clear whether firearms were used in any of those killings.
Tuesday's incident took place in Quarry Bay Park on Hong Kong Island at about 3 p.m.
The local Apple Daily newspaper said the dispute appeared to have been financial in nature and that the suspect appeared calm as she was being taken into custody with a hood placed over her head.
Source: AP