Two violent attacks this week involving psychiatric patients show the need for a more comprehensive policy for treating the mentally ill, a top psychiatrist says. Compounding the problem was the city's lack of doctors qualified to treat people who are mentally unstable, according to Dr Lee Wing-king, a member of the Hong Kong College of Psychiatrists' council. "We are starting to see the consequence of the doctors shortage," Lee said yesterday. On Thursday, an outpatient at Castle Peak Hospital in Tuen Mun went home to eat dinner with his family at Sam Shing Estate. Police said that at about 8pm, the man, 42, armed with a chopper, attacked a security guard at the estate. Several passers-by heard the victim's cries for help, managed to subdue the attacker and called police. The patient reportedly told a neighbour: "I chop people because I am happy." Another neighbour said they believed the man brought the chopper to carry out an attack on a target chosen at random. A shopkeeper in the area was not overly alarmed, saying: "There is nothing to worry about. No one expects this to happen." She said the man came to her shop twice on one day and he seemed normal. The man's brother and cousin lived at the public estate, while his mother passed away two years ago. The man has been arrested on suspicion of wounding and possession of imitation firearms. A spokeswoman from the Castle Peak facility said he had been receiving treatment at the hospital since 1993, and his last check-up was on December 11, when he was found to be stable. On Tuesday, a mentally ill woman whose family had insisted on discharging her from hospital - against medical advice - strangled her son and hung herself at their Taikoo Shing home, police said. But it would be wrong to portray people receiving treatment as especially violent, Lee said. Patients were less likely to be violent than anybody else. Outpatients were assessed and deemed fit to leave institutional care for brief periods, but often they could not return home permanently because of the family situation. "It is possible that something suddenly triggers the [undesirable] action in the patient," he said. "But most of the time, the patient will display symptoms over several weeks before their situation takes a sudden turn for the worse. Staff at the centre and family should be able to spot something is wrong." In August, college president Professor Linda Lam Chiu-wa said Hong Kong needed 700 psychiatrists to meet a World Health Organisation guideline, but the city had only 275 psychiatrists.