“Our colleagues are following up this lead,” a police spokeswoman said on Monday, confirming a report in the Rheinpfalz newspaper.
The newspaper quoted an eyewitness from a residents' meeting on Saturday who said that he saw workers smoking cigarettes before the blast at the town in Rhineland-Palatinate.
Gas company Gascade said that they couldn't comment on the rumours, but asked people to report anything that they might have seen to investigators.
GALLERY: Explosion rocks Ludwigshafen
On Friday, Gascade director Christoph von dem Bussche said that a “qualified construction company” had been hired to uncover the pipeline before it exploded.
Responding to criticism that gas was still flowing during the building work, he said it was only normal to shut it off “when the pipeline is being worked on directly.”
There had been no sign of a leak in the pipe before the start of the digging, von dem Bussche said.
The explosion on Thursday killed one worker and injured 23 people.
Sixty homes were damaged, 38 so seriously that they are no longer habitable. Eighty vehicles were also damaged.
SEE ALSO: Ludwigshafen explosion kills one