The CBI was asked last week by the Supreme Court to investigate the multi-crore scam and the death of at least 36 people linked to it. The central agency's RP Agrawal, a Meghalaya cadre officer, will head the investigation.

BJP chief Amit Shah landed in Bhopal early this morning, sparking speculation about a "damage control" exercise in the state, where his party is in power under Chief Minister Shivraj Singh Chouhan.

The BJP has, however, said Mr Shah is on a "regular visit." It said he would attend a day-long review meeting of a party membership drive and will then return to Delhi this evening.

Mr Chouhan welcomed Mr Shah at the airport today. Mr Chouhan emphasised over the weekend that Mr Shah is not in his state to discuss the Vyapam scam that has besieged his government.

Sources say so massive is the scam that it will take the CBI team months only to take a hand over from the state police on investigations conducted so far. It will begin by taking all files in its possession and will meet officers of a special task force or STF that conducted the investigation.

Mr Chouhan and the BJP have made it clear that the three-term Chief Minister will not oblige the Opposition, which wants him to resign over the Vyapam scam. The Congress says Mr Chouhan must resign to ensure an impartial inquiry.

Last week the Chief Minister buckled under pressure and requested his state's High Court to order a CBI investigation. But he has maintained that the state police has conducted an excellent probe so far. "There was a burden in my heart...I am relieved that now the CBI will probe and get to the truth," he said.

BJP's Madhya Pradesh unit president Nand Kumar Chouhan said on Sunday that the chief minister is "as holy as the river Ganga" and the CBI investigation would prove this.

About 2,800 people have been arrested in the Vyapam scam which refers to an alleged collusion by top politicians, bureaucrats and others that saw vast amounts of money being paid to allow imposters to take qualifying exams for government jobs.