Since Saturday, three women, all in their 30s, have been found in their ransacked apartments in two districts in the New Territories. A fourth was found on Hong Kong island yesterday but there are no details about this case.

The first two were robbed and strangled, one with a hose, while the third was certified dead with no apparent injuries early yesterday.

'We are adopting a very open-minded approach. We will rigorously pursue all lines of inquiry,' said police superintendent Steve Li, when asked whether a serial killer may have been responsible.

'We can't rule out the possibility that either one or more persons carried out these crimes.'

Murders of prostitutes are rare in Hong Kong. In 2003 and 2004, a retired Chinese soldier killed two sex workers during a visit there.

Zi Teng, a help group for sex workers, said that the three victims were among 1,800 women who advertised in local newspapers, offering services rendered in the privacy of their own apartments.

The so-called 'one flat, one phoenix' set-up lowers the chance of prosecution, compared with working out of a brothel, but often leaves women vulnerable to dangerous clients, Zi Teng said.

While there are no official statistics on the size of Hong Kong's sex industry, experts say there are at least 100,000 women working at any given time - most of them a transient pool from China's impoverished inland provinces.

Local TV footage showed police yesterday combing vice dens and urging vigilance.

'With such grave crimes having taken place, we are taking them very seriously and are actively investigating,' said police commissioner Tang King Shing.

REUTERS