(LONDON) — A search and rescue operation is underway after a 65-foot crane collapsed onto an under-development apartment block on Wednesday.

“A 20 meter crane [65 feet] has collapsed onto a block of flats under development and into two terraced houses on Compton Close,” London Fire Brigade Assistant Commissioner Graham Ellis said in a statement. “Our Urban Search and Rescue crews are undertaking a complex rescue operation and using specialist equipment to search the properties.”

“This is a multi-agency response and is likely to be a protracted incident. I would ask people to avoid the area,” he added.

Four people have so far been confirmed to be injured, according to the authorities.

“Two of these patients were treated for head injuries and taken to hospital,” the London Ambulance Service tweeted. “We assessed the other two patients but did not take them to hospital.”

The fire department was called at 2:39 p.m., and crews from surrounding stations descended on the scene. The London Ambulance Service tweeted that they had dispatched number of teams to the site of the collapse.

Aerial footage from the site shows the crane laying across an apartment block, with a section of the crane having smashed through the roof of an adjacent house.

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