Five HS2 workers were rescued with one hospitalised suffering neck and back injuries on Saturday after an incident at the Northholt vent shaft site in London.
Police and emergency services were called to the Mandeville Road site next to Northolt Tube station on Saturday just after 10am to rescue the workers.
The five men were recovered after an hour with one urgently airlifted to hospital, and the others treated at site for minor injuries and then later sent to hospital for checks.
All construction work has now halted at the site while the Health & Safety Executive investigates the incident.
Skanska Costain Strabag JV are responsible for the design and construction of the Mandeville Road ventilation shaft and headhouse.
A spokesperson for HS2 said: “Our thoughts are with the individuals involved in the incident, and we thank the ambulance service and the police for their assistance and support.
“We are working with our construction partner and the relevant authorities to understand the cause of the incident.
“All construction work at the site has stopped and a thorough investigation will be carried out.”