The workers were reportedly putting up a billboard on the sixth floor of a mall when the steel wires holding the platform snapped, plunging them to their deaths on Wednesday.
The fourth worker was a Bangladeshi, the police said, without revealing the identity of the victims.
According to the reports, the workers had started their shift at an early hour in order to adapt to the midday break rule for summer months that came into effect in mid-June, which prohibits workers from working between 12.30 pm and 3 pm.
An official at the Kuwaiti Hospital said they had received three dead bodies and an injured worker, who died in the hospital after several hours in the intensive care unit.
Hamid Al Mansouri, director general of Ansar Mall, told the media the four workers were putting up a signboard.
"They were not employed by us, but by a contracting firm that specialised in advertising," he said.
"It is now up to the police to investigate who is responsible for the incident, but there were safety concerns because the workers were not equipped with safety belts," he said.
The Sharjah police is investigating the incident.
