Mas Selamat, 47, is the alleged leader of JI's Singapore cell and has been accused of plotting to fly a hijacked aircraft into Changi airport and another plot to attack the US embassy.
He escaped from the toilet in the visitor's centre at Singapore's Whitley Road detention centre where he had been taken to meet his family.
|Mas Selamat is accused of plotting|
several attacks in Singapore [Reuters]
He is described as walking with a limp and authorities believe he is unlikely to be armed.
The escape led to an apology from the Singaporean government and a manhunt involving thousands of policemen.
Al Jazeera's Hamish MacDonald, reporting from Singapore, said security forces were scouring the landscape in what is probably the country's biggest manhunt.
He said Mas Selamat may have already fled north to Malaysia or across the sea to Indonesia, potentially safe havens where he is likely to find sympathy and support.
Apologising for the incident, Wong Kan Seng, Singapore's home affairs minister, said "it should never have happened".
"An independent investigation is under way and we should not speculate on what and how it happened," he told the country's parliament. "Security at the centre has been stepped up."
Malaysia and Indonesia have pledged to co-operate in the manhunt for Mas Selamat.
Indonesian security officials said they will work with Singapore to prepare for the likelihood that the fugitive may try to cross the sea to its territory.
Mas Selamat "would think Indonesia is the safest place" where it would likely be easier to hide, Nasir Abbas, a former JI operative who now works closely with Indonesian police, said.
Musa Hassan, the chief of the Malaysian police, said his forces were on the lookout and have informed border authorities, but have not made any other special arrangements to tighten border security.
"We have not received any special request from
|Singapore has stepped up land, sea|
and air security [Reuters]