Constable Jagbir died on the spot while his colleague Narendra was critically injured in the incident and is battling for life at a city hospital, police said.
"The incident occurred at around 2 AM on Monday when the two constables were on night patrol on their bike and found some persons sitting in an auto in L block, gali no.7," said a police official.
The policemen found their activities suspicious and questioned them. When they could not come up up with satisfactory answers, the two constables left their bike and sat in the auto to take them to nearby Vijay Vihar police station, he said.
The suspects, who were around three to four in number, then opened fire on both the constables from close range and fled, police said.
Jagbir died on the spot while the other constable, who sustained bullet injury in his back, was rushed to a nearby hospital where his condition is said to be serious, he said.
An FIR was registered under sections of murder, attempt to murder, Arms Act and others and several teams fanned out to nab the unidentified attackers.
Senior officials reached the spot immediately and Crime Branch and Special Cell have also been roped in to probe the case, police said.
The attackers seemed seasoned criminals as they even took away the policemen's arms with them, police said.
On Saturday night, three men had opened fire on two constables in Connaught Place area. No one was injured in the incident and one of the attackers was arrested.