Ma, 28, a boutique salesman on the same floor, said one of them pointed the gun at the other. He said the unarmed man challenged his gun-toting colleague to 'shoot if you have the guts'. Then the unarmed man rushed him, and the gun went off.

Ma, who was five metres from the men, said: 'The shot was loud. It echoed in my ear. I immediately hid behind a door and told others to hide.'

The pair continued arguing for about five or 10 minutes until more than 20 heavily armed police officers in bulletproof gear arrived and subdued them. Some officers pointed guns at the men while the others pushed them to the ground.

Another witness, Rex Lim Ser-siong, 20, who was shopping in a clothes store, said he heard a very loud gunshot. 'I smelt gunshot and I saw smoke.' Security staff at the mall then started to evacuate the people in the mall.

Tsang Yu-man, 55, who was eating at a restaurant nearby, heard the shot and waiters asked them to stay inside. He said: 'I was not very scared.'Another witness, student Katayee Chan Pui-ying, 18, said: 'I was just about to leave a restaurant but was told by the waiters to remain inside. I didn't hear the shot, but when I looked out I saw officers rushing in. I wasn't that scared'. She had to wait in the restaurant for 30 minutes before being allowed to leave.

Chief Inspector Sammual Lam Siu-wah said the shell had left a hole in the ceiling, and lead shot scattered over the floor. But there was no other damage. 'This is a serious case and we are conducting an in-depth investigation. A guard, aged 36, who allegedly opened fire was arrested'. The other guard was 40.

After the incident, police officers helped transfer the security container the men were supposed to be guarding to a vehicle sent by the security firm. The mall as well as sections of Great George Street and Gloucester Road were cordoned off until early this morning.