Guernsey arrivals into Jersey must now isolate for at least ten days.
The island has been moved from amber to red under Jersey's travel rules, as of 30 January.
Travellers will be required to undertake a PCR test on arrival (day zero), day five and day 10, and must isolate until they receive a negative result from all three.
Until now, Guernsey was the only jurisdiction not to be given red status, and therefore the only place you could travel from without needing to complete the highest level of quarantine.
But, following a resurgence of cases within the Bailiwick, stricter measures have been introduced.