STOCKHOLM: Swedish authorities on Wednesday kicked off the country's largest-ever crisis management exercise on what to do in the event of an accident at one of its nuclear plants.

The exercise will last until April and involve some 6,000 people from 70 government and emergency agencies, businesses and police, Helena Lindberg, the director general of the Swedish Civil Contingencies Agency, told reporters Wednesday.

"We have nuclear power in Sweden and have the mission as an authority to make sure we are well prepared, regardless of what happens," she said.

The exercise scenario started with the simulation of a sudden stop early Wednesday in two of the three nuclear reactors at the OKG nuclear plant in Oskarshamn, in southwestern Sweden.

It would later include a nuclear waste accident that would force authorities to plan for evacuations and increased communication with the public.

For the simulation, authorities interacted via a fake emergency website which also included fake news reports and concerned citizens posting alarmed comments on the "xbook" and "kvitter" fake social media sites.

"We previously practiced nuclear accident preparedness but we did it during office hours and really just practiced the chain of events ... and did not try out how such an accident would affect all sectors of society," Lindberg said.

"There is always concern because people can't see or touch radiation. It's important to practice how to communicate in those cases," she added.

Sweden's parliament passed a landmark bill last June allowing the country's nuclear reactors to be replaced at the end of their life spans instead of simply ending nuclear power when they expire.

However, the exercise launched Wednesday had been in the planning since November 2009, Lindberg said.

It was prompted by a 2007 report by the Swedish National Audit Office which found that "government agencies responsible have not ensured ... a good level of preparedness for managing the consequences of an accident at a Swedish nuclear power plant."