Two people have been killed and two seriously injured in an accident during building work on a bridge over the Twente canal near Lochem.

One of the white bridge arches, which was being moved into place by crane, broke loose and plunged to the ground, hitting several people as it fell.

The work is part of a ring road for Lochem, which includes two new bridges. Building company Bam was due to put the arches for one bridge – almost 140 metres long and 25 metres high – in place on Wednesday morning.

According to a reporter for regional paper De Stentor, the accident happened when one of the arches had been wynched to maximum height between two cranes.

“Something snapped and there was a very loud bang. The arch began to swing and then plunged to the ground,” Nieke Hoitink said. As it fell hit hit scaffolding where several workers were standing, knocking some of them to the ground.

The accident was seen by between 40 and 50 people who had turned up to watch the arches being lowered into place.  The road has now been closed to prevent sightseers reaching the location.

Prime minister Mark Rutte has offered his condolences to the families of the two men who died. The other two victims are being treated in hospital.