Manhole covers flew high into the air on Sturenkatu in Helsinki's Vallila district on Thursday morning just after 9:00.
According to the Helsinki Rescue Department, the cause was a leak of methane gas. Duty Fire Chief Ville Mensola reported that the natural gas buildup from a leakage arising out of telecommunications excavation work had probably caught as a result of some kind of spark, and the explosion had projected the metal drain-covers into the air.
After the incident, which caused some consternation to eyewitnesses but no injuries and only some damage to one car that was struck by a flying manhole cover, the fire service opened other covers in the area in order to release any other possible buildups of gas.
Director Jarko Alanko of Gasum, responsible for Helsinki's gas network, reported on Thursday afternoon that the cause of the incident was as yet unknown, but that the possible area affected had been narrowed down and was very localised. Supplies of gas in the area were unaffected.