Case numbers have soared and Germany on Wednesday registered its highest rate of infection since the pandemic began, with almost 40,000 cases in a day.
"We have to act right now," said Christian Drosten, who described a real emergency situation.
Doctors in the intensive care Covid ward at Leipzig University Hospital warn this fourth wave could be the worst yet.
One patient here, a woman in her 20s, has just given birth. Her baby is fine, but staff say they don't know whether she'll survive.