Travellers entering Denmark and Sweden will have to provide a negative coronavirus test from late December, irrespective of vaccine status.
A majority of the Danish parliament's epidemic committee on Thursday rubber-stamped a government proposal put forward by Health Minister Magnus Heunicke.
There are a number of exemptions for border communities, including for residents of German border state Schleswig-Holstein, people travelling on business, children under 15 and people who can prove they have recovered from coronavirus in the past six months.
The testing requirement goes into effect on Monday in Denmark and is initially in effect until January 17.
An antigen test must be no more than 48 hours old on arrival and a PCR (polymerase chain reaction) test no more than 72 hours old. For Danish residents, a test can be taken 24 hours after arrival.
Infection figures in Denmark keep reaching new highs, with the Omicron variant spreading rapidly and already dominant, according to Heunicke, whose country is busy providing booster jabs.
In Sweden, all foreign visitors aged 12 and older must have a negative test on them when they arrive, starting on Tuesday.
It must be no more than 48 hours old and both PCR and rapid tests are valid, the Swedish health authority said.
There are exceptions for commuters.
Sweden, which had chosen a special path with relatively moderate restrictions since the pandemic began, currently has one of the lowest incidence rates in the EU. But a quicker spread due to Omicron is now expected.