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STOCKHOLM (Reuters) - Twelve people were injured on Thursday when a bridge under construction in central Sweden collapsed, trapping workers under the debris, emergency services said.

The accident took place in Ludvika, a small town around three hours northwest of the capital. Of those hurt in the bridge collapse, four were seriously injured, authorities in the region of Dalarna said in a statement.

“Rescue workers and police are working at the scene but its very difficult because of all the debris. We have to be very careful,” police spokesman Henrik Olars said.

Local authorities said no workers were believed to remain trapped in the rubble from the bridge that was being constructed by Swedish construction group Skanska across the railroad in the city center.

“We take this extremely seriously. Our focus is now on those hurt in the accident. People are already heading to the scene to support and to begin an investigation of what has happened,” Edvard Lind, a Skanska spokesman, told news agency TT.