Home Affairs Minister Wong Kan Seng, urging against speculation, said an independent investigation into the security lapse was under way, and findings would be presented to Parliament when the probe was completed.

In the meantime, security at the Whitley Road Detention Centre has been stepped up after Mas Selamat Kastari, 47, escaped just before a family visit, when he asked to go to the toilet.

From security specialists and MPs to those in coffee shops and Internet chatrooms, the reaction was similar - shock and concern over how a well-known and dangerous figure, who walks with a limp, could escape in broad daylight.

Dr Teo Ho Pin, head of the Government Parliamentary Committee for Home Affairs and Law, said this incident was likely to impact on Singapore's standing in security matters.

'Security protocol needs to be constantly reviewed and we cannot be complacent,' he said.

He urged the authorities to look into the protocol at detention centres and the prisons as well, and suggested regular independent audits as well as scenarios to 'test' the systems.

Dr Teo was among the MPs who posed questions on the matter in Parliament yesterday.

Members of the security industry also questioned how such a security breach could have occurred.

Said Mr Ignatius Kang, general manager of security agency Apro-Asian Protection which has more than 700 employees taking care of 100 sites: 'It's very surprising because of who he is. I would imagine that they would have taken a lot of precautions to avoid this.'

A retired prisons officer with 30 years of experience said the escape was all the more alarming because he would have expected that there was likely to be more than one guard watching over such detainees at any one time.

He expected security cameras and other monitoring devices to have been in use to detect even silent communication, such as hand signals between detainees, or detainees and guards, even in places like the toilet.

And it was also likely that high-profile prisoners would not be allowed to see more than 3 to 5 per cent of the entire complex, making it difficult for them to plan an escape.

Mr Jeffrey Seah, director of the Security Industry Institute at Temasek Polytechnic, said: 'It looks like he may have taken advantage of the fact that we are quite civilised in our treatment of detainees, unlike some other places.'

Most of the 500 netizens on The Straits Times online site at www.straitstimes.com pressed hard for an explanation of what had happened.

Some recounted the recent incident where national serviceman Dave Teo allegedly walked out of an army camp with a rifle, and questioned if security protocols in all sensitive installations islandwide needed to be reviewed and stepped up.

Dr Kumar Ramakrishnan, head of the Centre of Excellence for National Security, said that security agencies cannot afford to let their guard down, because one slip-up is all it takes.

And Singapore was not alone in being dealt such a blow. He recounted the escape of Omar Farouq - a key Al-Qaeda operative - from a high-security facility in Afghanistan run by the United States.

Imam Syed Hassan Alattas, head of Ba'alwi Mosque, said that while he never expected something like this to happen in Singapore, he still had confidence that the authorities would re-arrest Mas Selamat.

To help find him, one posting on www.straitstimes.com contained this suggestion: 'I think it is worth having the phone providers MMS the photo of the wanted man to every cellphone.'