It is due to increased spread of infection that Malmö, Lund, Helsingborg and Gothenburg have been yellow marked in Denmark.
Danes who have traveled in southern Sweden are asked to be extra careful, and to test themselves after they have returned home from their stay abroad.
For Danes who are not fully vaccinated, there is a requirement for a covid test when returning home.
Restrictions soon gone
The new recommendations come a week after the announcement that all Danish restrictions will be lifted from 10 September.
The Minister of Health Magnus Heunicke (S) then stated that the restrictions can be reintroduced if the situation worsens.
The number of patients admitted to Danish hospitals for covid-19 on 31 August was 147.
A total of 2,587 corona-infected people have died in Denmark.
14 Danish covid deaths have been reported since 26 August.