NEW DELHI - Forty five power plants in India are operating with critically low coal inventories, government data showed, as monsoon rains disrupt supplies and electricity demand rises amid hotter-than-usual weather linked to El Nino.

The number of plants with coal stocks below 25% of their required inventory or with critically low stocks to generate power for less than three days has risen sharply from 31 at the end of July, the data as of August 25 showed.

Of the affected plants, 40 are domestic coal-fired plants, according to data on the website of Central Electricity Authority, a think tank linked to the federal power ministry.

Heavy rainfall in some of the key coal-rich Indian states, including Odisha, Jharkhand and Chhattisgarh has hit mining and slowed the transportation of the fuel for power plants, industry sources said.

"There has been a significant (inventory) drawdown, particularly through August, resulting in stocks falling 19% from end-July levels," commodities consultancy BigMint said.

Coal stocks at power plants stood at 30.95-million tons, equivalent to around 10 days of operational requirement, compared with 12 in July, BigMint said.

The lower coal stocks come at a time when the South Asian country is headed for its weakest monsoon since 2009, with uneven El Nino-linked rainfall driving up electricity demand in parts of the country.

"The uneven monsoon has driven power demand, primarily for air-conditioning. But coal supplies are running hand-to-mouth," an official at the country's largest thermal power producer, NTPC told Reuters.

"There is a need for five to six rakes at some plants, but we are receiving only half that number," the NTPC official said.

India has received 12% less rainfall than normal so far this monsoon season, leading to greater reliance on coal-fired power generation, particularly during the night when cooling demand remains elevated.

As a result, the power ministry has asked some of the coal-fired power plants to delay planned maintenance of units until the supply situation becomes clearer, a senior ministry official said.

The sources could not be named because they were not authorised to speak to the media.