Germany can expect “further significant attacks” after a lorry ploughed into crowds at a Berlin Christmas market on Monday killing at least 12 people, a police chief has warned.

Head of the federal criminal police office Holger Münch said Germany remained on “high alert” with police unclear whether a man arrested in connection with the attack is actually the perpetrator.

German police confirmed they are treating the incident, that injured at least 48, as a potential act of terrorism, however there has been no claim of responsibility so far.

“We need to work on the assumption that an armed perpetrator is still on the loose. As a result of this we are on high alert,” Mr Münch said at a press conference delivered by federal prosecutors.

"Currently we have one suspect but we are not sure whether he is the perpetrator and we don’t know whether there is only one. We have not found the weapon and that leads us to being in a high state of alert. Our investigations are ongoing to see whether there are other perpetrators that we need to arrest.”

It came as Germany's top prosecutor, Peter Frank, said the massacre could have been carried out by more than one person, adding that the suspect in custody "may not have been the perpetrator or belong to the group of perpetrators".

He also said terrorism as a motive was still just an assumption based on the similarities to the Nice terrorist attack.

Sources told Die Welt newspaper a Pakistani man detained near the scene of the massacre in Breitscheidplatz is not believed to be linked to the atrocity, meaning the attacker could still on the run. The man has denied any involvement in the attack.

"We have the wrong man," the newspaper quoted a Berlin police official saying. "And therefore a new situation — that the real attacker is still at large and can do more harm.”

Mr Münch suggested that if no video emerges with a claim of responsibility, it could suggest the attacker acted as a “lone wolf”.

Police presence has been increased at Christmas markets across Germany and officers have been armed with machine guns and protective vests.

However, Germany’s Interior Minister Thomas de Maiziere said Christmas markets and other big events should continue to take place following the incident.