The mishap occurred at about 11.30 AM when cylinders exploded triggering a blaze in the chemical manufacturing unit of Probace Enterprises at Shivaji Udyog Nagar of MIDC phase-II area in Dombivli (East).
Such was the intensity of the blast that the shock wave generated by it shattered window panes of adjoining buildings and shocked people were seen running helter-skelter, an eye-witness said.
"The death toll stood at five and the number of injured is 140," said District Disaster Control Officer Dinesh Kurhade.
Probace Enterprises mainly deals in hazardous chemicals.
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Due to the explosion, roof of some of the houses in the vicinity flew away while some huts were damaged. The explosion has created a big crater at the site.
Among the injured are those who were hit by flying glass shards.
District Collector Mahendra Kalyankar said a huge operation was underway for clearing the debris whereas the injured people were admitted in local hospitals.
Chief Minister Devendra Fadnavis visited the blast site and also the hospital where some of the injured are admitted.
"State government will bear all the expenses for their medical treatment," he said, adding that an in-depth enquiry will be conducted into the incident.
Fadnavis said, "this is a serious and major incident whose impact was felt in a long distance. The government would conduct a detailed inquiry".
Industries Minister Subash Desai said the chemical units in the belt would be kept shut for eight days from tomorrow.
The impact of the explosion was felt in an area of around five kilometres in which many vehicles were damaged.
Over a dozen firefighters from Thane, Kalyan, Ambernath, Ulhasnagar, Badlapur and Navi Mumbai were rushed to the spot to extinguish the flames.