In its latest travel warning update, the foreign ministry put Bulgaria's Blagoevgrad, Dobritch and Black Sea tourist hotspot Varna on its list of places where infections were rising rapidly.
Seven places in Romania — Arges, Bihor, Buzau, Neamt, Ialomita, Mehedinti and Timis — were also added.
This means that travellers entering Germany after visiting these sites must take a coronavirus test on arrival unless they can produce a test taken in the previous 48 hours.
Germany uses the yardstick of 50 new infections per 100,000 residents in the last seven days to determine if a country or region should go on its high-risk list.
It recently added three regions in Spain to the list in a blow to the fellow EU member state.
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The compulsory testing for people returning to Germany from risk countries begins this weekend, as fears grow over rising case numbers blamed on summer holidays and local outbreaks.
“It is already the case that travellers from risk zones are obliged to either go into a two-week quarantine or provide an up-to-date negative test result,” Health Minister Jens Spahn said at a press conference on Thursday.
From Saturday, “travellers entering Germany will have to bring a test result with them or be tested on arrival”, he added, confirming once again that the tests would be paid for by the government.
Spahn said test stations would continue to be set up at airports, and testing facilities will also be made available when entering Germany by train or car.
Currently, people in Germany coming back into the country from elsewhere can be tested free of charge for the virus within 72 hours of arrival.
But the government has decided to make tests mandatory for those coming from high risk regions in a bid to control the spread of coronavirus.
Currently, most countries in the world are classed as risk areas by Germany, including the USA and Brazil.