Visitors to Hangzhou may no longer feel like having landed in "Paradise on Earth" after the local government said on Monday that surveillance cameras would be installed in thousands of taxis in the city.

The cameras will record video as well as audio activities, and are aimed at ensuring better service quality and security, the city's transportation authorities said.

The number of spy cameras has increased dramatically in our cities over the past few years. We are being watched and photographed almost everywhere we go - in supermarkets, banks, buses, subway stations, gas stations, star-grade hotels and even street corners.

A few years ago, the Shanghai municipal government announced that it would install 200,000 surveillance cameras in the city alone by 2010. The actual figure could be reached much higher by now given the hyper-security alert before next year's 2010 World Expo. Still it does not mean spy cameras can be installed anywhere and in any numbers. Very few people taking a taxi would feel comfortable facing a spy camera. Besides, a camera would not only make most people uneasy, but also invade their privacy.

Those who support the move, such as police, argue that such cameras are an effective way to monitor abnormal activities and identify criminal suspects. They say such devices are especially necessary in today's world threatened by terrorist attacks.

But no one knows what percentage of criminal cases is solved or how many terrorists have been caught because of spy cameras. The success rate disclosed in some countries is actually very low. But the cost of installing such cameras and the public sacrificing its privacy is very high.

What is troubling is that no proper law on surveillance cameras exists. Where can a spy camera be installed and where would it constitute an intrusion of privacy? And who should be able to access the videotaped material?

Last year's Shanghai subway scandal serves as a case in point. A subway staff uploaded on the Internet a video clip from a surveillance camera that showed a young man and woman locked in a kiss on a platform. The case shocked the people and created a public uproar.

Hangzhou, of course, is not the first Chinese city to have cameras installed in taxis. Some taxis in cities such as Chengdu in Sichuan province, Xi'an in Shaanxi province, Shenyang in Liaoning province and Urumqi in the Xinjiang Uygur autonomous region have already done so despite public concern. But the impact on Hangzhou is likely to be stronger because of its importance as a tourism as well as commercial center. It will trigger another national debate on public security and personal privacy.

Hangzhou certainly wants to rethink if its move will make tourists feel less like being in "Paradise on Earth".