The four dead workers were Pakistani and Bangladeshi nationals, Gulf News reported.
"The intensity of the fire was very strong because the materials being burned were extremely flammable," said Brigadier Abdullah al-Suwaidi, director-general of Sharjah Civil Defense.
"The fire broke out at the pesticide factory and spread to the adjacent wood workshop but the exact cause has not been established until we carry out an investigation. We were able in six hours to get the fire under control," he added.
Al-Sajja police are investigating the incident.
Four of the injured workers were being treated at al-Qassimi and al-Kuwaiti hospital, Gulf News reported.