Thieves have made off with £100,000 worth of scaffolding from a Keepmoat building site in Hull.
The raiders hit the former Amy Johnson School site where Keepmoat has just started on a new housing development.
Police believe a forklift truck from the site was used to lift the pallets on to their getaway vehicle.
Police Sergeant Julian Hart said “Metal theft nationally is on the rise and in Hull, we have also been experiencing an increased number of metal thefts from houses, gardens and commercial businesses.
“This is a particularly high-value theft. We are informing scrap dealers about it so they can report any suspicious metal being brought into their premises to the police.
“This tactic has led to a number of arrests in recent months.”
Keepmoat said the incident hasn’t caused any delays at the site.
A Keepmoat spokesman said: "The site does have a security presence at all times. Someone is there 24/7.
"But it is a large site. We are having a look at the security arrangements in light of what has happened.
"Although it has been an inconvenience, this theft will not affect the building programme."