A crane being used to restore the Queen Juliana bridge in the Dutch city of Alphen aan den Rijn collapsed onto a number of nearby buildings, damaging at least five houses.
Initial reports said at least 20 people were injured but later reports indicated that the number of injured may be much lower.
One man has been pulled alive from the rubble already. Rescuers, along with sniffer dogs, would work deep into the night combing the scene for any other victims who might have been trapped, said Ton Koot, a spokesman for the local fire department.
"We hope that the number of victims stays at this one man who was taken to hospital with hip problems," Koot said in a telephone interview.
#hvnl #alphenadrijn pic.twitter.com/pQM6mwz9TF— Pieter de Graag (@PieterHVNL) August 3, 2015
Earlier, 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 stabilizing the situation so rescue workers can go in," Koot said.
Two teams usually deployed to overseas disasters such as earthquakes were at the scene with five specially trained sniffer dogs.
Live beelden van de rampplek #Julianabrug #AlpenaandenRijn http://t.co/75xJXU6nDW pic.twitter.com/TCAlbXGI8Z— Omroep West (@omroepwest) August 3, 2015
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 onto 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.
[video id=dqZjdydjpmt1LiztwmCJ9efJzvBuRjtV]
"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.
Vaker problemen met Julianabrug Alphen http://t.co/SW6b29sCFG pic.twitter.com/5MQ45Okyal— Joey van Maanen (@JoeyvanMaanen) August 3, 2015
The local municipality 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.
Additional reporting by Mashable