”Suddenly there was a bang and the whole windscreen just vanished,” said coach driver Gunnar Norberg to Sveriges Radio (SR).
The coach was forced to a stop and the Södra länken ('The Southern Link') tunnel had to be closed off.
”I went outside, only to see this huge iron bar that came through the ceiling and went all the way into the ground. It was quite obvious that someone was drilling above,” Norberg continued.
Stockholm police are treating the incident as a possible criminal offence, a case of negligence or alternatively of endangering the public.
”It's a company carrying out ground work for a potential building project, which drilled in the wrong place. The drill has penetrated a tunnel and a pipe came loose and fell down hitting a vehicle,” said Sasse Sahlin at one of the city's traffic management centres to news agency TT.
However, the workman who was carrying out the work above told SR that Södra länken tunnel wasn't on the maps of the city he had received form the city council.
He had heard on the radio that traffic had been halted in the tunnel, but didn't put two and two together, according to SR. He was only notified of the accident when the police arrived.
To Norberg, in the tunnel, it was obvious what was going on above.
"You could hear that it was someone drilling. There was a bloody racket down there in the tunnel. And they kept on drilling, obviously unaware of what had happened. So I called Radio Stockholm."
All traffic was later stopped leading to the Södra länken tunnel.
”An inspector has since checked the damages and now traffic has been let in again with limited access,” Sahlin said to TT.
No one was apparently hurt during the incident, despite two trucks crashing in to the drill.
Södra länken is a 6 kilometre Stockholm motorway, of which 4.7 kilometres runs underground.
It was inaugurated in 2004.