Chief Minister Yogi Adityanath, who was away in Mauritius on a three-day official visit, ordered that necessary steps be taken for rescue and relief.
The project supplies electricity to Uttar Pradesh, Haryana, Himachal Pradesh, Jammu and Kashmir, Punjab, Rajasthan, Chandigarh, Delhi and Uttranchal.
People injured in the explosion being taken to hospital.
In their statement, NTPC said there was a "sudden abnormal sound" before an opening emerged in a pipe, followed by a release of flue gases and steam.
Chief Medical Officer of Rae Bareli Dr KK Singh said that so far eight bodies were brought to district hospital and several injured workers were admitted to the hospital.More news: Frozen Metallica Mashup Has Kristen Bell & Dave Grohl Rocking Out
All that Ganga Prasad, a labourer at the NTPC plant in Unchahar at Raebareli, remembers was that there was a loud explosion and then he heard cries all around him. "The NTPC's senior management is rushing to the site to coordinate the efforts".
Gandhi represents the Raebareli parliamentary constituency in the Lok Sabha. The government also announced Rs 2 lakh compensation for the family of those workers who have died and Rs 50,000 for the grievously injured and Rs 25,000 for other injured workers.
The CM also expressed his condolences on the death of NTPC workers in the accident.
The power's first unit was commissioned in 1998 and the last and sixth unit was commissioned in 2006.
The plant, which started generating power in 1988, has five power generating units of 210 MW each. He is a member of 101Reporters.com, a pan-India network of grassroots reporters.