The incident occurred when the tanker got stuck under a flyover along a canal on the Doraha Bypass Road, about 25-km from here, they said.
"Five persons died from inhaling the gas and over 100 others complained of breathing problems.
"Those affected after inhaling the gas have been admitted to various hospitals in Ludhiana. Barring 2-3 persons, all were stated to be out of danger by the doctors," Ludhiana Police Commissioner Pramod Ban told PTI over the phone.
Police said that all the deceased are male adults with two among them having been identified as Satpal of Doraha and Avtej Singh of Jalandhar.
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The tanker bears a Gujarat licence plate, police said, adding that the incident occurred on the Delhi-Ludhiana highway.
Khanna SSP Gurpreet Singh Gill said that the incident was caused by the negligence of the driver. The tanker got stuck under the flyover and its valve got damaged, resulting in the leakage, added Gill.
Doraha SHO Rajnish Kumar Sood said that the bodies have been shifted to a hospital in Ludhiana.