The 13-year-old boy remains in hospital after being hurt at the old Stocks Blocks site in Garforth on Saturday evening.
Emergency services, including the Hazardous Area Response Team, were sent to the scene in Ninelands Lane just before 7pm.
Yorkshire Ambulance Service (YAS) said it had dispatched a rapid response vehicle and ambulance to the scene along with its Hazardous Area Response Team and the Yorkshire Air Ambulance.
A YAS spokeswoman said the boy had been taken to Leeds General Infirmary by road ambulance for further treatment.
The 13-year-old boy from Garforth was seriously injured and remained in hospital, West Yorkshire Police said earlier today.
The full circumstances of the incident are now the subject of an investigation by the Health and Safety Executive (HSE).
A spokeswoman said: “HSE is aware of the incident and the local construction division team in Leeds is making enquiries but we cannot comment any further at this time.”
The site was previously used for the construction of building blocks by Stocks Bros (Buildings) Limited, which traded as Stocks Blocks until the company was dissolved in April 2016.
It remains under the ownership of Thomas Armstrong, a holding company of Stocks Bros.
Company secretary Paul Armstrong said: "It's a very regrettable incident and our thoughts are with the young lad and his family.
"There's an investigation ongoing and that's as much as I can say until we know any more."
The land has been earmarked for redevelopment as part of the council's masterplan, with the nine hectare brownfield site being allocated for housing.
Developer Redrow Homes lodged a planning application in January to build 238 homes, the vast majority of which would have four bedrooms.
City planners are yet to make a decision on the application, which was opposed by two local councillors and dozens of residents.