STOCKHOLM, May 17 (Xinhua) -- After severe delays and cancellations due to a fallen overhead contact line on Wednesday, trains started operating again on Thursday afternoon in Sweden.

The Swedish Transport Administration said traffic should resume as normal on all four tracks between Uppsala and Stockholm, Swedish Television reported.

That was after train traffic was down to 50 percent capacity and passengers were allowed to board any available train, regardless of which rail company they had bought their tickets from.

Bengt Olsson, head of press at the Swedish Transport Administration, said the fact that it took 24 hours to resolve the problems was because the work on the contact line was complex and had unintended consequences.

"Putting up an overhead contact line doesn't take that much time, in itself. But it was along a 200-meter stretch, a fire broke out and we had to await a green light from the emergency rescue services," Olsson said.

The fire caused additional electricity problems that had to be identified and resolved before normal train traffic could resume on Thursday.