Emergency services were called to a Leeds building site after a 35-year-old man suffered a suspected heart attack.
The man was not at work at the time, and was believed to be in a lift when he suffered the medical episode.
The incident, which happened at a site close to the The Playhouse at Quarry Hill in Cecilia Steet, saw a number of emergency service vehicles descend on the area with the man given CPR before an on-site defribulator was used.
He has since been taken to Leeds General Infirmary where he remains in a critical condition. His family have been informed of the ongoing situation.
A spokesman for Caddick Construction, which runs the site, said: "Emergency services were called this morning (Friday) to the SOYO site in Leeds after reports of a 35 year old sub-contractor suffering a suspected heart attack. He was not working at the time and was at ground floor level.
"He was given CPR and an on-site defribulator was used before he was taken to Leeds General Infirmary where he remains in a critical condition. His next of kin have been informed and our thoughts are with them at this extremely worrying time.
"The HSE has been informed as a matter of course."
A spokeswoman for Yorkshire Ambulance Service added: "We were called at 9.42am to a medical incident on a construction site in St Cecilia Street.
"We dispatched an ambulance, a rapid response vehicle and our Hazardous Area Response Team (HART). One patient was conveyed to hospital."
