At least four workers were killed and one injured in a blast in a chimney at the state-run National Thermal Power Corp (NTPC) power station here on Friday morning, police said.According to police officer Saheblal Attar, the explosion occurred around noon in the chimney of the 1,320 MW plant, on the outskirts of the city."As per preliminary information, four workers have perished in the blast and at least one is injured," Attar told IANS. "Rescue teams and fire brigade have been rushed to the disaster site."This is Maharashtra's first ultra-thermal power generation plant deploying super-critical technology, making it eco-friendly and is being built at a cost of around Rs.10,000 crore investment by NTPC.