Indian police shot dead one of the country's most wanted gangsters on Friday just a day after his dramatic arrest, sparking accusations of a staged extra-judicial killing.

Officials said Vikas Dubey, detained for the killing of eight police officers, was shot as he tried to escape a police vehicle while being driven to his home city in the northern state of Uttar Pradesh.

Within hours of TV stations carrying images of his bloodstained body lying in a hospital, rights lawyers and activists alleged that police had killed Dubey to prevent him revealing his connections with powerful people.

“This is the most blatant case of extra-judicial killing. Dubey was a gangster terrorist who may have deserved to die. But [Uttar Pradesh] police have killed him to shut his mouth,” Supreme Court lawyer Prashant Bhushan wrote on Twitter.

“Will we allow police to kill anyone without a court trial?” Utsav Bains, another Supreme Court lawyer, added.

Senior opposition Congress party leader Priyanka Gandhi said the people “protecting” Dubey were still free.

Dubey, aged about 50, was accused in more than 60 murders, attempted murders and other cases. He was said to have shot dead an Uttar Pradesh state minister inside a police station in 2001.

Despite those cases and his reputation for ruthlessness, Dubey has built considerable local political links over the past two decades.

On July 3, eight officers were gunned down when Dubey's gang staged an ambush on a police team aiming to arrest him.

A nationwide manhunt was launched, during which five of Dubey's associates — including his bodyguard nephew — were killed.

The gang leader finally gave himself up in a temple in Madhya Pradesh state on Thursday.

According to the police account, the car taking him to Kanpur early Friday overturned on a wet road and he tried to escape.

“Dubey has been killed in an exchange of fire after he snatched the pistol of our men and tried to flee after firing at them. Four of our men are also injured,” Kanpur police inspector general Mohit Agarwal told reporters.

Nirjhari Sinha, founder of a civil rights organisation in Gujarat state, said his death had revived memories of staged killings there.

“History repeats,” she wrote on Twitter. “Dead gangsters can't speak about their political patronage.”

For decades, shoot-outs were staged to bypass India's judicial system when police battled armed separatist movements in West Bengal, Punjab, Indian-occupied Kashmir and remote northeastern states.

More recently, suspects accused of violent crimes have died in custody.

Last year, police in southern India shot dead four men accused in the horrific rape-murder of a 27-year-old woman.