As of today, visitors to the U.S. from 35 countries must request visa waivers via a new online clearance service.

The Electronic System for Travel Authorization (ESTA) has been up and running since last August but becomes compulsory today. Previously, travellers from most European nations, Japan, South Korea, Brunei, Singapore, Australia and New Zealand could enter the U.S. without a visa simply by filling out a paper I-94 form on the ship or airplane. Now, all such travellers must request clearance in advance via the ESTA Web site.

U.S. Immigration officials say that the ESTA system is easy to use and clearances usually come back to the traveller within minutes of their request. But they also warn that clearance is a must and that travellers needed clearance may be delayed at their point of entry to the U.S. if they fail to get clearance in advance via the new online system.

Visitors to the U.S. under the Visa Waiver Program can stay there for up to 90 days. For full details, visit the Know Before You Go’ Web site.