Patrons visiting one of the Netherlands' red- light districts may soon find themselves on camera.

One by one, authorities in cities across the country are stepping up their efforts to regulate, scrutinize and generally clean up the country's sex business.

This week the mayors of the cities of Alkmaar and Utrecht followed moves by Amsterdam in 2007 to toughen regulation and reduce the ability of the sex trade to act as cover for and cause of other illegal activities.

Authorities have cited drug-dealing, money-laundering and the trafficking of women as crimes that are to be targeted.

Closed-circuit television (CCTV) surveillance of sex districts is just one method that has been proposed.

The mayor of Utrecht, a city in central Netherlands, announced on Friday that the entire area of Zandpad in the city would be placed under CCTV surveillance in an effort to tackle the trafficking of women.

'We need to know which women are being forced to work as prostitutes,' Mayor Aleid Wolfsen explained, 'or if women are abused or exploited. Filming the area, and knowing which pimps are connected to which women, will increase our opportunities to help the women.'

Wolfsen said that two independent studies had concluded that between 50 and 90 per cent of the women working in the Utrecht prostitution zones were not doing so voluntarily.

On Zandpad Street alone, some 900 prostitutes are working in 140 prostitution venues, housed in typical Dutch houseboats along the Vecht river.

Prostitution itself is legal in the Netherlands, with companies operating brothels being required to obtain a licence before they can open for business.

Brothels are required to list individual sex workers as employees. It is a bureaucratic procedure, which doesn't provide the authorities with information on whether or not the women were employed voluntarily.

This is why Wolfsen wants to change the law, 'requiring individual prostitutes to apply for a licence themselves.'

Utrecht will also make it easier for prostitutes to report crimes and criminals to the police and get help, Wolfsen said.

The activities of prostitution firms themselves are also to be brought under greater scrutiny.

A 2003 law, which obliges businesses to prove that assets used in their trade have been obtained legally, can help to cut underground activity associated with brothels.

On Tuesday, Mayor of Alkmaar Piet Bruinoge announced that the city would not be renewing the license of the JE Nool company, which operates 95 out of the 125 brothels in Alkmaar's Achterdam Street.

Authorities in Alkmaar, north of Amsterdam, said that JE Nool did not fulfill the terms of the 2003 law, known as BIBOB.

In 2007, BIBOB was used by the city of Amsterdam to close down a substantial number of its brothels, claiming the venues were used for money-laundering and related crime.

BIBOB also authorizes local authorities to check the brothel owner's criminal record, and to investigate whether the company was ever involved in criminal activity.

The city of Alkmaar says it has no intention of closing down the prostitution zone entirely.

'If brothels observe Dutch law, they will be given a licence,' Bruinoge told Dutch media.

But he added the city was determined to fight the increased crime rate in the area.

Alkmaar police have now been authorized to stop passers-by in the prostitution zone, and perform so-called random 'preventive searches' for weapons or hard drugs.

Utrecht authorities have also said they will use the law in their own red-light districts.

However, in what might be interpreted as a sign of the waning of sex zones in the Netherlands, Amsterdam's red-light area is itself experiencing something of a transformation.

In 2007, 18 buildings previously used as sex venues were bought by the city - to be used as an up-and-coming centre for haute couture.