A huge fire at an Indian oil depot that has killed at least six people and injured 150 will be allowed to burn out as firefighters have little hope of dousing it, officials said Friday.

Another six people are trapped in the depot near the city of Jaipur in the western state of Rajasthan where the fire has been burning for about 20 hours since it broke out Thursday evening.

"The fire has to die down. There is nothing else one can do. There is no other solution or alternative," federal petroleum minister Murli Deora told reporters.

Dense clouds of black smoke billowed out of at least three oil tanks which were ablaze.

The six dead were all workers at the depot.

Thousands of people living near the oil depot have been evacuated, and power supplies to the surrounding areas switched off. Train services on tracks running near the oil depot have also been halted.

Army troops have been deployed to help in the firefighting operations at the depot, 10 miles south of Jaipur, which stores gasoline, kerosene and diesel fuel for several state-owned oil companies.

"The fire is massive. We are finding it a bit difficult to douse it," Deora said.

Huge explosions were heard before the fire broke out and flames leaped into the sky. The blaze was visible from over 16 miles away.

At least 35 firefighting teams, including some from the Indian capital of New Delhi, 220 miles to the north, were sent to battle the flames, which burned through the night.