German coronavirus infections are spreading exponentially, up 20% in the last week, an expert at the Robert Koch Institute for infectious diseases said on Tuesday, adding that the risk of AstraZeneca's vaccine was relatively low.

"We are exactly on the flank of the third wave. That can no longer be disputed. And at this point we have eased the restrictions and that is speeding up the exponential growth," RKI epidemiologist Dirk Brockmann told German ARD television.

Merkel and state leaders agreed a phased easing of curbs earlier this month along with an "emergency brake" to let authorities reimpose restrictions if case numbers rise above 100 per 100,000 on three consecutive days.

On Monday, the number of cases per 100,000 rose to 83, up from 79 on Sunday and 68 a week ago, and the RKI has warned that metric could reach 200 by the middle of next month.

Germany on Monday suspended use of AstraZeneca's COVID-19 vaccine, making it the latest of several European countries to hit pause following reports of blood coagulation disorders in recipients.

The decision followed a recommendation from the Paul Ehrlich Institute (PEI), Germany's authority in charge of vaccines, following seven cases of thrombosis, including three deaths.

Brockmann said it made sense to explain the relative risks to the population, noting that 1,000 people in a million had died of COVID-19, compared to possibly 1 in a million from complications associated with the vaccine.

"In the risk groups, the risk of dying of (COVID-19) is much, much higher. That means it is probably 100,000 times more likely to die of (COVID-19) than because of an AstraZeneca vaccine," he said.