German police evacuated two train stations in Munich late on Thursday, saying on Twitter they had received a tip regarding a planned militant attack on New Year's Eve in the Bavarian capital.
A police spokeswoman declined to give further details, saying a search for possible suspects had been launched.
"Actual lead that in #Munich a terror attack is planned. Please avoid crowd gatherings as well as the central train station and the Pasinger train station," read a translation of the German tweet.
It added: "Pasinger and central stations have been evacuated. Trains are no longer running. Please follow police instructions."
Another tweet from the police said: "We note explicitly once again that we take the threat very seriously. Please remain alert."
The measures added to security fears in Europe heightened by Belgium's decision to cancel New Year's Eve celebrations in Brussels, citing a suspected plot to carry out an attack in the capital.
Belgian police said late on Thursday that three people had been arrested for questioning as part of an investigation into the plot.
German police canceled a friendly soccer game between Germany and the Netherlands in the city of Hanover on Nov. 17 hours before it was due to start because of fears of a planned bombing attack.
The match was due to have been held four days after the attacks in Paris that killed 130 people. After the cancellation, German government officials struggled to give the soccer-crazy country a convincing explanation, saying only that it had been the right decision.
No arrests were made and no explosives were found after the cancellation.
German Chancellor Angela Merkel has rebuffed pressure to clamp down on migrant arrivals along Bavaria's border with Austria, which critics say allowed Islamic State to smuggle in militants to carry out attacks in Europe.
Opposition to her stance grew at home and abroad after two of the suicide bombers in the Nov. 13 Paris attacks were found to be have been carrying fake Syria passports.
In an apparent effort to allay those concerns, Germany said on Thursday it would start holding personal hearings for asylum seekers from Syria as of Friday, reversing a policy of granting almost automatic refugee status for Syrians.
Syrians have since the end of 2014 enjoyed a simplified asylum process, which has exempted them from personal hearings.
Security concerns were also heightened in the United States where memories were fresh of the attacks in Paris and in San Bernardino, California, where 14 people were killed on Dec. 2.
In New York on Thursday, police were taking extraordinary measures to ensure security for the traditional New Year's Eve dropping of the crystal ball in Times Square, where more than a million people were expected.