A train carrying $51 million in banknotes has been robbed in a carefully organized heist in southern India.

Around $750,000 worth of cash was stolen when thieves cut through the metal roof of one of the carriages and took almost two full chests of banknotes.

Police believe that a gang of between six and eight people was involved, although they are still unsure whether the thieves smuggled themselves onto the train at the start of the journey and cut their way out, or cut their way in while it was in motion. Guards sitting in the next carriage reportedly heard nothing.

Inspector General of Police M Ramasubramani told reporters the criminals "created a manhole and then sneaked one after the other and lifted the bundles [of cash] to the roof before taking them away."

According to the BBC’s South Asia editor Jill McGivering, the sheer weight of Indian paper money may have limited the thieves’ takings.

“Clearly only a fraction of the money has gone: they only opened two crates out of 200,” she said. “But apparently the amount of money they removed came to more than 20 tons in weight, [because] these included many small denominations.”

The route from Salem Town to Chennai is used by the authorities to transport old and damaged banknotes to Chennai to be destroyed. The train is reported to have been heavily guarded.

From PRI's The World ©2016 PRI