Police have launched a massive manhunt following the killing of an officer who interrupted a drug deal.

Tremaine Wilbourn, 29, faces a first-degree murder charge over the death of Officer Sean Bolton, 33, in Memphis, Tennessee, on Saturday night. Police have warned that he is armed and dangerous.

Wilbourn was a passenger in a car being investigated by Officer Sean Bolton on Saturday night, Memphis police director Toney Armstrong said.

He said Officer Bolton came across a 2002 Mercedes parked illegally in a neighbourhood in south-east Memphis and shone his squad car's spotlight on the vehicle.

Officer Bolton got out of his car and walked towards the Mercedes, Mr Armstrong said. Wilbourn then left the Mercedes, confronted the policeman, and the two got into a physical struggle.

Wilbourn, on supervised release after serving a federal sentence for robbery, took out a gun and opened fire, hitting Officer Bolton multiple times, Mrr Armstrong said. The officer died in hospital.

Wilbourn and the driver fled after the shooting and the driver later turned himself in. He was released without charge.

Officers found about 1.7 grams of marijuana inside the car, which would have probably just resulted in a misdemeanour prosecution and a fine for Wilbourn, Mr Armstrong said.

Officer Bolton is the third Memphis officer to be shot dead in just over four years.