New York (CNN Business) In the surest sign yet that the trade war is hurting the American economy, manufacturing activity contracted for the second month in a row in September, falling to a level not seen in 10 years.

The Institute of Supply Management's closely-watched manufacturing index dropped to 47.8 in September, its lowest level since June 2009 and worse than what economists had expected.

The index measures month-to-month changes in the industry. A reading above 50 denotes growth in the sector.

"Global trade remains the most significant issue, as demonstrated by the contraction in new export orders that began in July 2019," said Timothy Fiore, chair of the ISM's manufacturing business survey committee.

Making matters worse, the contraction in September was steeper than it was in August, when the sector contracted for the first time in three years because of higher prices that factories pay for materials and weaker global demand.

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