The incident took place around 6:15 PM when the cash van, which belonged to a private company, reached an ATM at Paharganj.
"As a couple of its staff went inside to refill the ATM, the others, who were supposed to guard the van, also went around. When they returned, Rs 23 lakh were found to have been stolen from the van," said a police official.
The van had left its office with Rs 87 lakh cash earlier today and had reached the Central Bank ATM after refilling a few ATM machines around Central Delhi, he said.
"CCTV footages of all the cameras installed in the area are being examined. Driver, custodians, security guard and other company staff are being questioned," the official said.
A case has been registered at the Nabi Karim police station," said Additional Commissioner of Police (Central) Alok Kumar.
Investigators said they were surprised to know that the van which had so much cash was left unguarded and are probing the possibility of an insider's role, besides other angles.