An Israeli tourist found on the tracks of the shuttle train at Hong Kong airport had squeezed through a 20cm gap between the platform screen door and the train compartment.
The Airport Authority said yesterday the 27-year-old man had sneaked through the gap onto the tracks after the shuttle he was travelling in pulled in at the west hall of Terminal One on Tuesday afternoon.
Security measures on the airport rail system have been stepped up after the incident, which halted services between the terminal's east and west halls for about four hours.
Police meanwhile said there were no indications the tourist was drunk when he was spotted on the tracks just before 4pm on Tuesday.
But investigations are continuing into whether he was high on drugs. The visitor, who was pepper-sprayed as he was arrested, was still being held for questioning last night. He has not been charged.
Two policemen from the airport's security unit and three airport staff were injured during the arrest.
The airport's general manager for technical services, Ricky Leung Wing-kei, said surveillance cameras captured the unauthorised entry of the traveller, but did not say how long it had taken to find him. 'The design and operation of the whole system comply with international standards and are approved by the Electrical and Mechanical Services Department's railway branch,' he said.
After the incident, extra staff members were sent to guard the platforms as a temporary measure to prevent people from squeezing through the gap and jumping onto the tracks.
It was the first incident of its kind since the free shuttle train service, which takes visitors between the airport's boarding gates and immigration counters, came into operation in 1998.
'We are investigating with the manufacturer and the government's railway branch how we can improve this,' Leung said.
But Terminal One general manager Michael Yuen Ying-kit said it was 'not regarded as a security breach'.
He said the passenger had gone through normal security and clearance channels to enter the airport's restricted area.
Last night, the MTR Corp said sensors had been installed at gaps on its system that were big enough for a person to enter.
Once triggered, all trains entering and leaving the platform would be stopped.