The incident took place at around 10 am in Patparganj area when the petrol pump manager, Sanjay Kumar, was going to deposit the money in a bank, police said.
Police are suspecting the role of an insider in the case.
Sanjay in his statement before police said that when he came towards the main road, he noticed the men standing near their motorcycles.
When Sanjay went a few metres ahead, the four men started their motorcycles and stopped him and looted Rs 21 lakh at gun point. Since the robbers were masked, the victim could not see their faces.
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Police are checking the CCTV footages of the area to identify the robbers.
The incident occurred at a place which is just 300 meters away from the office of the Deputy Commissioner of Police (DCP) of East district. The petrol pump is situated in Anand Vihar and is owned by a person identified as Sameer.
A case under appropriate sections of the IPC was lodged at Madhu Vihar Police Station.
"We are questioning other employees of the petrol station for possible leads. A manhunt has been launched to nab the accused. Further investigations are underway," a police official said.