German police said on Friday that a key railway line in the western city of Düsseldorf had been hit by a second arson attack in two days, hours after a fire in a cable duct caused widespread disruptions on the same stretch.

Police told the German DPA news agency that the incendiary device used was of the same type as the one discovered following Thursday's blaze, which shut down a major line between Düsseldorf and the nearby city of Duisburg, adding that damage has once again been caused to the line.

"We presume that both attacks were carried out at the same time," said a police spokesman, confirming that officers had finished gathering evidence by midday and that repair work would begin.

The second incident was discovered 1.8 kilometers (1.1 miles) north of the first near the town of Angermund.

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German trains: how long will distruption last?

German rail operator Deutsche Bahn spoke of "vandalism" and warned of train diversions and delays. It said disruption would likely continue until Saturday morning at least.

Among the train services affected are those serving Düsseldorf International Airport, Germany's fourth-busiest airport.

Local media reported long queues at Düsseldorf and Duisburg central stations on Friday morning as commuters tried to make alternative travel arrangements — but there was reportedly no sense of chaos, with many people seemingly having expected disruption due to Thursday's sabotage.

Has anyone claimed responsibility?

Responsibility for Thursday's incident was claimed by a self-proclaimed "Angry Birds Commando" which posted a statement on the left-wing platform Indymedia reading: "Many things would work infinitely better without the industrial system."

"Based on our authorities' current assessment and understanding of this act of sabotage, it was left-wing extremists who are trying to bomb us back to pre-industrial times," said Herbert Reul, interior minister for the state of North Rhine-Westphalia.

The Angry Birds Commando "is known to our authorities as a left-wing extremist campaign. It has carried out several acts of sabotage in the Dusseldorf area in recent years," Reul said at a press conference in the city.

No individual or group has yet claimed direct responsibility for Friday's incident, although the statement posted on Thursday did refer to "several attacks" in the Düsseldorf region.

With 700-800 daily connections, the Düsseldorf-Duisburg route forms part of one of Germany's busiest railway lines, with the disruption having knock-on effects as far as Berlin, Frankfurt and the Netherlands.

Edited by: Elizabeth Schumacher