THE police have assured the public that they will thoroughly pursue all leads, as the search for fugitive Mas Selamat Kastari enters the fourth day.

Police have received a number of tip-offs and calls on sightings of the militant leader of the Singapore Jemaah Islamiyah (JI) terror network since his daring escape from Internal Security Department's custody at the Whitley Road Detention Centre on Wednesday at 4.05 pm.

The manager of a petrol station at Whitley Road was reported as having told two Chinese evening newspapers, Lianhe Wanbao and Shin Min Daily, on Friday that he saw a man resembling the escaped detainee Mas Selamat about one hour after he bolted from the nearby detention centre.

He said the man's upper body was bare and he was wearing brown pants with the letters 'WRC'. He was seen struggling and limping up a flight of steps on the hill slope which leads to the Bukit Brown Chinese cemetery.

Police said they had received similar information from his co-worker at the petrol station at about 5.15pm.

A thorough search around the vicinity was immediately conducted but the man could not be found.

'The vigilance of the manager and his prompt action to call the police are commendable,' said police in a statement released at close to midnight on Friday.

'The search for Mas Selamat Kastari is on-going. The police assure that all leads are thoroughly pursued.'

Members of public with any information on his whereabouts should call 999 immediately. They can also email police at spf_police_information@spf.gov.sg.

Their identity will be kept strictly confidential, assured the police.

In the extensive manhunt for the 1.58 tall terrorist, who walks with a limp on the left leg, police are leaving no stones unturned.

Over the past three days, every lead from a stolen SingPost delivery van to sightings of limping men were chased down until the police were sure there was no connection to the escaped detainee.

Police officers were at the Singapore Association of the Visually Handicapped (SAVH) on Thursday afternoon, checking on their closed-circuit television camera footage of the main road, Toa Payoh Rise. They spent over two hours watching the video and later made a copy which they took away.

SAVH executive director Edmund Wan claimed that he did not know what was in the footage, but The Straits Times understands that it showed a man limping along the road in the direction of Toa Payoh Lorong 1.

The man was wearing a T-shirt and white trousers and was caught on film at around 9.30 pm on Wednesday, over five hours after the escape. Other tip-offs by the public led to police sending out squads of officers.

On Friday morning, about 40 Gurkhas searched the thickly-wooded Bukit Brown Chinese cemetery near Lornie Road and did not find anything.

They later moved to the nearby Singapore Island Country Club and then to the Tree Top Walk at MacRitchie Reservoir.

Separately, a group of Singapore Armed Forces soldiers trudged into the forested area at Bukit Panjang, which runs to the Bukit Timah Nature Reserve. They were later reinforced by Gurkhas.

Thousands of posters, showing two photographs of Mas Selamat - one of him with moustache and goatee, and the other clean-shaven - have gone up across Singapore, asking the public for help to track him down.

The posters have been plastered at train stations, bus terminals, shopping malls and coffee shops across the island.

Residents in several estates, including the Caldecott Hill area, Clementi Park in Sunset Way, have also had leaflets stuffed into their mailboxes.