Memories of Switzerland's worst environmental disaster haunted the town of Schweizerhalle on Monday night, following an explosion at a factory owned by the Swiss pharmaceutical giant, Novartis.
Nobody was injured in the blast, which caused severe damage to the building in Schweizerhalle in canton Basel Country, blowing out windows and scattering glass over a radius of 50 metres.
Police said some 200 fire fighters were needed to bring the resulting blaze under control, and reinforcements were brought in from the nearby towns of Muttenz and Liestal.
The blast evoked memories of a fire which broke out at a factory owned by Sandoz - which later merged with Ciba-Geigy to become Novartis - in Schweizerhalle in 1986. That incident caused some 1,351 tonnes of chemicals to go up in flames, releasing a toxic cloud over Basel and polluting the Rhine.
At a press conference, Novartis spokesman Peter Marbet, apologised to the local population, but said the explosion was not as bad as had first been thought.
Hansjörg Wetter, chief of chemical production at Novartis, admitted that the company had no idea what caused the explosion. "We have no idea what happened, and we cannot resume production until the cause has been established."
He added that the factory had been producing medicines for the treatment of epilepsy for the past 10 years without incident.
The cause of the 1986 disaster - the worst environmental catastrophe in Switzerland's history - was never established.
swissinfo with agencies