At least eight persons were killed and more than 40 injured in an explosion at a boiler unit of the NTPC in Uttar Pradesh's Rae Bareli district on Wednesday evening, officials said.

The death toll is likely to rise as many more are feared trapped inside the 500 MW boiler unit at the NTPC, Unchahar, Additional Director General (ADG) Law and Order Anand Kumar said.

Eight bodies have been received at the district hospital, Chief Medical Officer K.K. Singh of Rae Bareli told .

A massive fire broke out inside and a huge ball of dust rose after the explosion, making rescue operations difficult, an official told . 

The unit was the sixth at NTPC and was commissioned on March 31 this year, a senior official said.

An alert has been sounded at the community health centre (CHC), district hospital and at other medical centres, after the accident. 

Chief Minister Yogi Adityanath, who is in Mauritius on a three-day visit, directed Principal Secretary (Home) Arvind Kumar to monitor the situation and brief him regularly. 

The Chief Minister has announced ex-gratia of Rs 2 lakh each to the families of those killed, Rs 50,000 each to those seriously injured, and Rs 25,000 each to those with less grave injuries.

Senior district officials and police officials are at the accident site and overseeing rescue and relief operations, a state government spokesman said.

Officials said the explosion took place in the boiler which is filled with water in tubes which are heated. This in turn creates steam which moves the turbines and generates electricity.