Mumbai: The deaths of 26 workers in an explosion at a government-run power plant in India's northern Uttar Pradesh state has highlighted safety concerns for daily wage workers tasked with high-risk jobs, campaigners said.

An explosion at the NTPC Ltd power plant in Rae Bareli district on Wednesday was one of the country's deadliest industrial accidents in years with more than 20 survivors battling for their lives.

An inquiry was ordered on Thursday to establish the cause of the blast.

Sanjay Kumar Khatri, district magistrate of Rae Bareli, told the Thomson Reuters Foundation that two plant supervisors died in the blast but most of those killed were daily wage labourers.

Government data shows that more than 80 percent of India's employed workforce is in the informal workforce that largely comprises rural and daily wage labourers who are hired off the road or through contractors supplying labour.

Campaigners said casual workers engaged in factories are rarely given sufficient safety instructions or training.

"Safety measures for them are rarely adequate," said Sandeep Khare, member of Informal Workers Rights Union in Lucknow, capital of Uttar Pradesh.

"When companies source labour through contractors, their responsibility towards them is very (much) less."

Officials of NTPC could not be immediately contacted for comment.

The government has announced it will pay compensation of 200,000 Indian rupees ($3,000) to the families of the workers who died in the explosion.

Social activist Nikhil Dey said there has been constant safety concerns at industrial plants acrossIndia because the most dangerous positions are filled with casual labour.

"More daily wage workers are being hired and they also account for most deaths (in such accidents)," said Umi Daniel, South Asia head of the migration division of non-profit Aide et Action International.