Armed men posing as officials from India's central bank have robbed a vehicle transporting 70m rupees ($800,000; £600,000) in the southern state of Karnataka, police say.

A massive operation has been launched to find the men who robbed the van in the heart of Bengaluru city in daylight.

The robbery occurred on Wednesday afternoon. Six men in an SUV stopped a cash transport van on a busy road as it was moving money between bank branches, Bengaluru police commissioner Seemant Kumar Singh told the BBC.

The van was carrying a driver, a cash custodian and two armed security guards.

Mr Singh says the robbers told the people in the van that they were officials from the Reserve Bank of India and needed to verify if they had the correct documents to transport such a huge amount of money.

The gang told the cash custodian and guards to leave their weapons in the van and get into the SUV, while the driver was instructed to continue driving with the cash, police said.

The SUV followed the cash van for a few kilometres before the gang forced the driver out of the van, made the cash custodian and guards get out of the SUV, transferred the cash at gunpoint, and fled.

The area had little CCTV coverage, and police are investigating if the gang used multiple vehicles in the operation.

The cash transportation service company has filed a police complaint.

The SUV used in the heist had a fake number plate and a sticker that read "Government of India", a police official told the BBC on condition of anonymity.

The official added that police were also investigating if the company employees had anything to do with the heist.

Karnataka Chief Minister Siddaramaiah told reporters that police have recovered the SUV used in the heist.

But Home Minister G Parameshwara has said that it is not yet clear which vehicle the suspects had used to escape.

"It was verified that they changed vehicles and moved the money," he told reporters.

He said he was confident police would solve the case soon, as they had with other recent high-profile bank robberies in Karnataka.

In May, 59kg of gold worth 532.6m rupees was stolen from a Vijayapura district bank using a duplicate locker key. Police have since recovered 39kg of gold and some cash, and arrested 15 people, including two former employees.