An under-construction chimney of Reliance Energy's Ultra Mega Power Project in Sasan collapsed on Thursday triggering a stampede in which six persons were injured, three of them seriously.<br/><br/>Singrauli Collector P Narhari said the under-construction chimney was 10 to 15 metre tall and it was supposed to be built 270 metres long. After the incident, some locals protested and tried to set fire to two vehicles.