Congress leader Rahul Gandhi on Thursday demanded a proper investigation to prevent incidents like the toxic gas leak from a chemical tanker in Surat which killed six people.

He also sent his condolences to the families of those who lost their lives in the incident and wished a speedy recovery to the injured.

"Condolences to those whose loved ones lost their lives due to the gas leak accident in Surat. I wish the other victims a speedy recovery.

"Proper investigation should be done to prevent such accidents in future," he said in a tweet in Hindi, tagging a news report about the incident.

Six factory workers died and 22 others were hospitalised after they inhaled toxic fumes leaking from the chemical tanker parked near a factory in Gujarat's Surat district in the early hours of Thursday, officials said.

The workers were in the dyeing factory, located in Sachin industrial area, when the incident took place, Surat Municipal Corporation's (SMC) in-charge chief fire officer Basant Pareek said.