The eight core sectors -- coal, crude oil, natural gas, refinery products, fertiliser, steel, cement and electricity -- grew by 9 per cent in September last year.
The growth stood at 5.8 per cent in August this year.
Production in crude oil, natural gas, refinery products and fertiliser has registered a drop of 1.1 per cent, 6.2 per cent, 2.5 per cent and 11.6 per cent respectively in the month under review, according to the data released by the Commerce and Industry Ministry.
These sectors had registered a growth of 13.6 per cent, 12.1 per cent, 10.7 per cent and 12.9 per cent in September 2013 respectively.
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Commenting on the numbers, rating agency ICRA said: "Although the core sector growth has slipped considerably in September in sequential terms, an earlier onset to the festive season is likely to have provided some boost to various sectors of manufacturing. Nevertheless, IIP growth is likely to have been subdued in September."
In January 2014, the eight core industry index registered an overall growth of 1.6 per cent.
During April-September, the eight sectors grew by 4 per cent, against 5 per cent in the year-ago period.