Germany received a tip that militants from Iraq and Syria were planning attacks in Munich on New Year's Eve but police have been unable to find the suspects and are not even sure if they exist, Munich's police chief says.

MORE: Manhunt underway after German terror threats

Hubertus Andrae told a news conference on Friday that German officials had received a "very concrete" tip late on Thursday that suicide attacks were planned at two train stations.

Police closed the stations about an hour before midnight, and reopened them hours later.
"We received names. We can't say if they are in Munich or in fact in Germany," Andrae said.

"At this point we don't know if these names are correct, if these people even exist, or where they might be. If we knew this we would be a clear step further. We have no information that these people are in Munich or in Germany," he added.

Bavaria Interior Minister Joachim Herrmann has said the tip, which media reports said came from French intelligence, indicated that the Islamic State militant group was behind the planned attacks.

The shutting down of the stations added to jitters in many capitals as Europe ushered in the New Year with heightened security after a year of militant attacks, the biggest of which killed 130 in Paris in November.

The stations that were shut were Munich's central station and Pasing station, some 8km away.

Andrae said the security alert level in Munich remained the same as it was before German authorities received the tip.

On their Twitter feed, Munich police said: "Good morning to those, who spent the night out in #munich! Thanks for staying calm and for your understanding concerning our measures."

Police said they had received information that five to seven suicide bombers were planning to take part in the attack.

The Munich alarm followed days of security warnings in Europe. On December 26, police in the Austrian capital Vienna said a "friendly" intelligence service had warned European capitals of the possibility of a shooting or bomb attack before New Year.

That tip, too, had included the names of several suspects.

In Belgium, authorities on Wednesday called off the usual New Year's Eve fireworks display in the capital, citing fears of a possible militant attack. Police said on Thursday they were holding three people for questioning over an alleged plot.