Chancellor Angela Merkel warned on Tuesday there could be no further relaxation of coronavirus restrictions while Germany grapples with a surge in new infections.
She urged Germans to follow the rules on hygiene precautions and reminded travellers returning from risk areas that quarantine was not an option "but a must" so long as they could not show a negative test.
"We are seeing that an increase in mobility and closer contacts are leading to a higher number of cases," Merkel told a press conference in Duesseldorf.
"I believe there can be no further loosening (of restrictions) at this point," she said in her first public comments on the pandemic since returning from her summer break.
Germany has fared better than many European neighbours in suppressing the virus so far but like elsewhere, the number of coronavirus cases has jumped significantly over the summer holidays.
Much of the rise has been blamed on returning holidaymakers as well as parties and family gatherings.
Germany has in recent weeks reported an average of well over 1,000 new cases a day, compared with around 350 in early June.
"This is a trend that cannot continue and must be halted," Merkel told reporters.
"When I say we need to pull in the reins I mean the rules need to be enforced very consistently."
Germany earlier this month introduced free, mandatory tests for anyone returning from areas deemed a high risk for COVID-19 infections, including tourist hotspot Mallorca.
People awaiting their results must stay in quarantine at home until the test comes back negative, Merkel said, warning that those who fail to comply face fines.
She also welcomed tougher checks on buses and trains to make sure passengers were wearing face masks and keeping a safe distance.
"If we comply with all of this, the good news is that much of public life can carry on. Everyone can do their bit," Merkel said.
- 'Very concerning' trend -
Large events are still banned in Germany until August 31, and Merkel's comments suggest organisers will face a longer wait before they can bring back the crowds.
German authorities have already refused to back plans for fans to return to football stadiums when the Bundesliga season starts next month.
Merkel said the priority was to "keep economic life going" to protect jobs and to keep schools and daycare centres open.
School children across Germany have started returning to the classroom after the summer holidays, facing a slew of new regulations such as staggered arrival times and mask wearing in a bid to contain the spread of the virus and avoid new school closures.
As of Tuesday, Germany had recorded a total of 225,404 coronavirus cases and 9,236 fatalities, according to the Robert Koch Institute (RKI) for disease control.
The RKI has called Germany's upward trend in infections "very concerning".