Travellers from countries normally granted visa-free entry to the United States will have to get visas if their passports do not have a bar code that can be read by a machine.
Holders of Hong Kong or British National (Overseas) passports will not be affected, as they are required to obtain visas to travel to the United States.
Under the policy, which takes effect on October 26, travellers from visa-waiver countries will also be required to enrol in US-Visit, a programme that uses biometric technology - such as digital photos and finger scans - to verify holders' identities.
The 27 countries exempt from the visa requirement are: Andorra, Austria, Australia, Belgium, Britain, Brunei, Denmark, Finland, France, Germany, Iceland, Ireland, Italy, Japan, Liechtenstein, Luxembourg, Monaco, the Netherlands, New Zealand, Norway, Portugal, San Marino, Singapore, Slovenia, Spain, Sweden and Switzerland.
Susan Stevenson, spokeswoman for the American consulate in Hong Kong, said as most of these countries already issued machine-readable passports, the new policy was unlikely to affect a large number of people.
'We are just concerned that there is a group of people out there who, for whatever reasons, do not have machine-readable passports and may be caught completely by surprise when they arrive in the US and have to be turned back,' she said.
Ms Stevenson said Canadian passport holders would not be affected as Canada had a separate agreement with the US.
She added that the machine-readable passport requirement was different from the biometric passport requirement, which is due to come into effect next October.