New Delhi, Oct. 27 -- A slowdown in India's core industries in September has raised fresh concerns about the momentum of industrial and GDP growth heading into the second half of the fiscal year.

The eight core sectors-coal, crude oil, natural gas, refinery products, fertilizers, steel, cement and electricity-form the backbone of India's industrial economy and weigh nearly 40% of the Index of Industrial Production (IIP).

In September, output shrank in half of these sectors, coal, crude oil, natural gas, and refinery products, reflecting weaker energy production and refining activity. Fertilizers, cement and electricity managed modest gains, though at a slower pace than before.

Steel alone defied the trend, expanding strongly year-on-ye...