The work team was drilling at Wollmar Yxkullsgatan, on Södermalm, to prepare for the installation of geothermal heating for a nearby hotel, but their drilling punctured the subway line and crushed the side panel of the driver’s carriage of a train that was waiting on the tracks.

“They drilled right down onto a subway train,” Lars-Erik Baarsen, station officer at Södermalms Police, told news agency TT.

After the workers had drilled to a depth of 20 to 25 metres, the team noticed that the resistance to the drill disappeared. “They then withdrew the drill and discovered that two-and-a-half metres of the drill was missing,” Baarsen said.

Meanwhile, down in the tunnel, the driver of the subway train was shocked when the side panel of his carriage was suddenly crushed by something from above.

Greater Stockholm Local Traffic Authority (SL) stated that it was either the drilling itself that crushed the panel or something the drilling pulled loose on its way down. The result was that the subway’s red line stood still for approximately one hour, from around 3.45pm.

No one was injured in the incident, including the driver. “We had amazing luck. It could have been really serious,” Per Ekberg, SL’s press officer, told TT.

The police have commenced a preliminary investigation into whether there may be grounds to lay charges over gross negligence causing a public danger.