German police are investigating a suspected political motive behind an alleged act of sabotage targeting a major train route connecting the port city of Hamburg to the capital, Berlin.

Fire broke out overnight at three locations in the northern Hamburg region, affecting shafts holding railway cables.

Hamburg police said investigators believe the fires were "set deliberately" and that a "political motive lies behind the crime." They added that investigators were seeking witnesses to the suspected crime.

German Transport Minister Volker Wissing described the suspected vandalism as "a form of terrorism," in statements to the German DPA news agency.

"It is only a matter of luck that no one was harmed," Wissing said, calling for harsh legal consequences.

What do we know about the incident?

An anonymous letter published on the far-left website Indymedia claimed responsibility for the incident, describing it as an act of "sabotage." The letter said it was a protest against "neo-colonial exploitation and earth destroying extraction of raw materials."

Police have yet to determine the authenticity of the letter.

Security head at German rail operator Deutsche Bahn Hans-Hilmar Rischke said they were in close contact with the authorities and that he hoped "those responsible" would be quickly apprehended.

"People who want to travel with us — with one of the most climate-friendly means of transport — are massively affected by train cancellations and delays and won't be able to reach their destinations," Rischke said.

How has the incident affected travel?

Trains on the main high-speed route between Hamburg and Berlin were canceled, as well as long-distance trains between Hamburg and Rostock. Deutsche Bahn said it was running a few trains to and from the capital on another route, which elongated the trip by around an hour.

A spokesperson said train traffic would likely not be restored until Saturday morning.

The DPA news agency reported that train commuters reacted with anger at the impact of the incident on their trips. However, many noted that Deutsche Bahn trains are often delayed, an issue which has persisted in recent years.

Company reports suggest that over a third of the operator's long-distance trains arrive at least 15 minutes late.

"The railroad itself is not very punctual. The fact that it's vandalism makes a difference," a 67-year-old man from Hesse in western Germany told DPA while waiting at Hamburg Central Station on Friday.

rmt/nm (AFP, dpa)