A former Danish gang leader who wrote a memoir about leaving his life of crime was gunned down within hours of launching his book.

Nedim Yasar was shot at least twice as he left the book launch in Copenhagen. police said. The gunman then fled the scene.

The 31-year-old was rushed to a nearby hospital in critical condition and died on Tuesday.

Yasar formerly led a gang known as Los Guerreros, Spanish for "warriors", which was involved in the drugs trade.

His book Roedder (Roots), about leaving the criminal underworld, was published.

Denmark's justice minister, Soren Pape Poulsen, paid tribute to Yasar, tweeting: "How sad and infinitely meaningless. I met Nedim once. I met a man who with all his heart wanted to create and new life and make a difference for others. My thoughts and compassion go to his friends and family."

He added: "It goes without saying that this terrible tragedy begs the question of whether we as a society have the right protection for those who want to step out of the shadows and back into society."

Police investigate the scene of the shooting after the book launch in Copenhagen (Bax Lindhardt/Ritzau Scanpix via AP)

Copies of Yasar's memoir 'Roots - A gangster's way out' displayed in a bookstore (BAX LINDHARDT/AFP/Getty Images)

Yasar was born in Turkey and came to Denmark aged 4.

He decided to leave his gang and join an exit programme after he became a father, Danish news agency Ritzau reported.

The former gang leader, who made a name for himself as a radio host after quitting, often spoke of his life experiences on his talk show.

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Police said Yasar told them he had been the victim of an attempted assault in 2017, after he quit the gang.