Police in Italy have arrested an Italian man over the slaying of a Nigerian vendor whose brutal beating on a busy beach town thoroughfare was filmed by onlookers without any apparent attempt to intervene physically.

Video footage of the attack has circulated widely on Italian news websites and social media, eliciting outrage as Italy enters a parliamentary election campaign in which the Right-wing coalition has already made immigration an issue.

"The murder of Alika Ogorchukwu is dismaying," Enrico Letta, a former premier and the head of the Left-wing Democratic Party, wrote on Twitter, naming the vendor who died. "Unheard of ferocity. Widespread indifference. There can be no justification."

Right-wing leader Matteo Salvini, who is making security the base of his campaign, also expressed outrage over the death, saying "security has no colour and ... needs to return to being a right."

Alika Ogorchukwu, 39, was killed on an Italian street as people filmed the attack on their phones. No one intervened to stop the murder.

Ogorchukwu, 39, a was selling goods on the main street of Civitanova Marche, a beach town on the Adriatic Sea on Friday, when his attacker grabbed the vendor's crutch and struck him down, according to police. Video shows the assailant wrestling the victim onto his back on the pavement as he fought back, eventually subduing Ogorchukwu with the weight of his body.

"The aggressor went after the victim, first hitting him with a crutch. He made him fall to the ground, then he finished, causing the death, striking repeatedly with his bare hands,″ police investigator Matteo Luconi told a press conference.

He later told Italian news channel Sky TG24 that onlookers called police, who responded after the suspect had fled and attempted to administer aid to the victim. An autopsy will determine if the death was provoked by blows, suffocation or another cause.

Police used street cameras to track the assailant's movements and detained a man identified as Filippo Claudio Giuseppe Ferlazzo, 32. He was being held on suspicion of murder and theft for allegedly taking the victim's phone.

Luconi said the assailant lashed out after the vendor made "insistent" requests for pocket change. Police were questioning witnesses and viewing videos of the attack. They said the suspect has made no statement.

Ogorchukwu, who was married with two children, resorted to selling goods on the street after he was struck by a car and lost his job as a labourer due to his injuries, said Daniel Amanza, who runs the ACSIM association for immigrants in the Marche region's Macerata province.

Amanza gave a different version of what happened, saying the attacker became infuriated when Ogorchukwu told the man's companion she was beautiful.

"This compliment killed him," said Amanza.

"The tragic fact is that there were many people nearby. They filmed, saying 'Stop,' but no one moved to separate them," Amanza said.

Macerata was the site of a 2018 shooting spree targeting African immigrants that wounded six people. Luca Traini, 31, was sentenced to 12 years in prison for the shootings, which Italy's highest court confirmed qualified as a hate crime.

Civitanova Marche's mayor, Fabrizio Ciarapica, met with members of the Nigerian community after hundreds demonstrated yesterday .

"My condemnation is not only for the (crime) but it is also for the indifference,″ Ciarapica told Sky. "This has shocked citizens."

Former Premier Matteo Renzi, who heads his own small party, called out political leaders for "instrumentalising" the attack.

- Coleen Barry, AP