Taxmen have unearthed undisclosed assets worth Rs 600 crore from 28 locations in Purnea town in the biggest income tax raid in Bihar since demonetisation last November.

Raids were conducted on a super-speciality hospital - Max 7 Hospital - and a few connected medical and educational institutions in Purnea town, around 320km northwest of Patna. The operations concluded on the night of April 22 but the amount of undisclosed assets may increase, sources said, because post-raid investigations are on.

Altogether 130 income tax officials participated in the operation with 100 policemen.

"We have discovered huge unaccounted investment in land, a proposed medical college, cash, jewellery, over 50 bank lockers and suppression of facts," Ashok Kumar Sinha, principal director, income tax investigations for Bihar and Jharkhand, told The Telegraph.

Max 7 Hospital has 13 directors and apart from the hospital premises, raids were conducted on the commercial and residential premises of 11 of the directors. Majority of them are doctors with flourishing private practices, nursing homes, diagnostic centres and a couple of coaching centres for medical and job aspirants.

"The doctors were also planning to open a medical college at Kasba in Purnea district," an income tax official said. "It was to be named Seemanchal Institute of Technology. Documents related to the purchase of several acres of land and massive investment have been recovered during the raids," one of the income tax officials associated with the raids said.

The official added that the raid has so far yielded around 5kg of gold, Rs 1 crore in cash and 200 bank accounts. Officials said the persons raided have accepted they had undisclosed income of Rs 26 crore.

"Of the 50 bank lockers seized, around 35 are yet to be opened. We are expecting gold, jewellery and cash from them. This is the biggest income tax raid in the state after demonetisation was announced on November 8, 2016," the official said.

It all had started after a deposit of Rs 1 crore in scrapped 500 and 1,000-denomination notes by one of the directors of Max 7 Hospital came on the radar of financial intelligence agencies. They passed on the information to the Bihar-Jharkhand income tax zone as part of 2,500 bank accounts with deposits of Rs 1 crore and above after demonetisation that need to be investigated by the taxmen.

"While investigating the account of Max 7 Hospital, we had thought it to be a routine affair, but the case turned out to be huge," a source in the income tax department said. "One link led to another and we quickly expanded the raid. We will now focus on other people connected to those who have been raided upon. There are several non-doctors among them."

The taxmen are also planning to investigate whether the investments being made in the proposed medical college was from doctors or people from other walks of life. They would also refer the case to the Enforcement Directorate and the CBI.