Tense moments were witnessed on Friday outside the prestigious South Block in Delhi, housing the Prime Ministers' Office, when the revolver of a policeman went off accidentally injuring a Delhi police commando.

The incident occurred around afternoon when Head Constable Suraj Pal and Delhi Police Commando Sanjay Kumar were about to start having lunch inside the roadside cabin located outside South Block.

According to sources, Pal, who is nearing retirement, was demonstrating to Kumar that the first chamber of his revolver is kept empty.

However while pressing the trigger, the bullet in chamber that was supposed to be empty, fired and pierced through Kumar's left thigh.

The prime minister was not inside the office when the incident occurred.

Pal was arrested by the police and and a case of negligence on duty was registered against him, a police spokesman said.

Kumar, posted in the Third Battalion of the Delhi Armed Police, was rushed to Ram Manohar Lohia Hospital where his condition is stated to be out of danger, the spokesman added.

"Only one shot was fired. We are investigating the matter," Deputy Commissioner of Police (New Delhi District) Anand Mohan, who visited the spot, said.

Senior Delhi police officials rushed to the spot to ensure that the investigations were being conducted properly.

"Yes, there has been an incident near the South Block office of the prime minister. Two constables were on duty at the cabin created for security personnel. While handling his .38 bore weapon, Pal accidentally fired it, injuring his colleague Kumar. The injured constable was rushed to the Ram Manohar Lohia hospital," Assistant Commissioner of Police Rajan Bhagat told rediff.com.

Additional Reportage: PTI