Chancellor Angela Merkel sounded the alarm on Saturday over the return of a "certain recklessness" as Covid-19 infection and death rates climb in Germany.

Increasing numbers of hospitals admissions with coronavirus "worry me a lot", Merkel told Sunday's edition of the Frankfurter Allgemeine Zeitung newspaper.

"It should worry all of us," she added, noting "again a certain recklessness" in Germany.

She defended the right not to be vaccinated but admitted at being "very saddened" that as many as three million Germans aged over 60 have still not had the jab.

"It could make a difference, for these people and the whole of society," said Merkel, who steps down soon after 16 years in office.

Infections took off with the arrival of autumn and on Saturday the Robert Koch health institute (RKI) reported 21,543 new cases and 90 deaths over the previous 24 hours.

Germany's seven-day coronavirus incidence rate crossed 145 infections per 100,000 people on Saturday, after hitting 100 a week before for the first time since May.

The vaccination campaign is marking time with RKI counting 55.5 million Germans fully vaccinated against Covid, or 66.7 percent of the 83 million population.

Health professionals have reported a new influx of infected people into hospital, mostly unvaccinated.

The president of the German society of hospitals Gerald Gass said the number of Covid patients entering hospital had jumped 40 percent in a week. Intensive care wards had 15 percent more cases.

"If this continues, we will soon have 3,000 patients in intensive care," he told reporters. And that would lead to restrictions on the normal functioning of hospitals such as delays for operations.

In a Forsa survey carried out for the health ministry and published Thursday, 65 percent of unvaccinated respondents declared there was "no way" they would take a Covid jab and 23 percent were "reluctant".

Some 89 percent said the risk of intensive care wards being overwhelmed had no influence over their readiness to be vaccinated.