Rescuers have pulled a survivor from under the wreckage of apartments and shops that were flattened after two cranes being used in the restoration of a bridge toppled on to a row of buildings.
One man was pulled alive from the rubble in the Dutch city of Alphen aan den Rijn, and rescuers including sniffer dogs are due to work deep into the night combing the scene for any other victims who might have been trapped.
Ton Koot, a spokesman for the fire department, said: "We hope that the number of victims stays at this one man who was taken to hospital with hip problems."
Earlier, Mr Koot said that 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.
"We are stabilising the situation so rescue workers can go in," he said. Two teams usually deployed to overseas disasters such as earthquakes were at the scene with five trained sniffer dogs.
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 and 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 authorities 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.