Combined stocks of thermal coal at 100 Indian power plants climbed 39% on the year to a new record high of 27.5 million mt Wednesday, enough supply for 18 days of coal burn, according to data released by India's Central Electricity Authority Friday.

Power plant inventories have been extending gains to new record levels since mid-March when stocks surpassed the previous 10-year record high of 23.33 million mt reached on August 22, 2013.

The stock levels were also almost 25% higher than a month ago, according to Platts data.

CEA's data showed that the number of Indian power plants with less than a week's supply of coal was 11, down from 14 a month ago and 22 at the same time last year. Of these, only five had inventories lasting less than four days of consumption, up from two on March 8, but down from nine a year ago, the CEA data showed.

The data also showed that, of the current coal stocks, 3.1 million mt was imported coal, more than doubling from the 1.4 million mt of imported coal on stock a year ago, as well as 14% higher than March 8.

This is the first time imported coal stocks at the power plants have climbed above the 3 million mt level since Platts data records of Indian power plant stocks began in July 2011, although inventories have consistently remained above the 2 million mt level since mid-January.

Market sources have been noting that the country's rail rake shortage is ongoing, although adding that power plants have been running at low capacity due to slow industrial production. They also said that Indian buyers bought a large amount of imported thermal coal in early March, as well as domestic coal from Coal India before the end of the April 2014-March 2015 financial year.