By European standards, Germany has experienced relatively low infection and death rates so far during the pandemic, but new daily cases have jumped in recent weeks.
They have now reached a record of 6,638, bringing the total since the start of the pandemic to 341,223, data from the Robert Koch Institute (RKI) for infectious diseases showed on Thursday.
The previous record daily increase was 6,294 on March 28, according to RKI data.
Germany's states agreed late on Wednesday to extend measures against the spread of the coronavirus to larger parts of the country as new cases soared, but Merkel warned even tougher steps may be needed.
German Health Minister Jens Spahn warned that people's behaviour in the coming days would determine whether they will be able to spend Christmas with their families this year.
"It's important to understand that we are not powerless against this virus. We can do something, we all can make a difference every day," he told Deutschlandfunk radio on Thursday.
"We can be the spoilsport for the virus if we are careful with one another and keep the number of new infections to a level we can handle."
Thursday's tally showed the reported death toll rose by 33 to 9,710.