Two cranes being used in the restoration of a bridge in the Netherlands have collapsed on to a row of buildings, flattening apartments and small shops.
More than three hours after the accident in the central city of Alphen aan den Rijn, it remained unclear how many people - if any - were trapped under the rubble.
"At the moment we don't know how many victims there are or if there are any," said Kees van Velzen, the acting mayor.
Local fire brigade spokesman Ton Koot said initial reports of between seven and 20 injured victims were based on estimates of the number of people who might have been in the houses when the cranes slammed into them.
He said one person had been taken to hospital.
"We are stabilising the situation so rescue workers can go in," Mr Koot said. Two teams usually deployed to overseas disasters such as earthquakes were at the scene with five trained dogs trying to sniff out people trapped in the wreckage.
Dramatic amateur video aired by national broadcaster NOS showed the towering orange cranes on a pontoon on the Rijn river carrying a large section of the bridge, when they begin to sway then topple on to houses, slamming through the buildings and sending a cloud of dust into the air.
The bridge section they had been carrying also appeared to land on the buildings.
"You see the cloud of dust rise - that is a terrible image and you think, 'Who is under there?'. You can't believe what you see," witness Dick van Smirren told NOS.
Local officials urged people to stay away from the scene to allow rescuers to carry out their work.
The Dutch Safety Board, which investigates serious accidents, said it was sending a team to the scene.