The soldiers have been sent to the main problem area, Ahmedabad. Earlier on Friday, they shot dead five rioters there.
The fighting started when a train full of Hindu protesters was set on fire by a mob of Muslims on Wednesday.
Curfews are in place across 26 cities in Gujarat state.
Hindus and Muslims are angry about a mosque which was torn down by Hindus in 1992, sparking riots which killed more than 2,000 people in India.
And now officials are worried this recent violence could spread across the country once more.