FRANKFURT, Aug. 15 — A bitter feud between rival southern Italian crime families erupted on the streets of a northern German city early Wednesday morning, as the police in Duisburg found the bullet-riddled bodies of five Italian men in two vehicles.

A sixth man died on the way to the hospital. The police said the men, ages 16 to 39, had been shot in the head outside an Italian pizzeria near the main train station.

Italy’s interior minister, Giuliano Amato, said the killings apparently stemmed from a vendetta between the families. Both families are part of a ruthless, secretive mob organization from Calabria known as ’Ndrangheta, which the Italian authorities now regard as a more sinister threat than the Sicilian Mafia.

(Funeral service workers collected the bodies of Italian men who were shot near a train station in Duisberg, Germany. )

Mr. Amato told reporters in Rome that one of the victims might have been involved in an earlier killing. He warned of an escalating mob war, saying, “We need to be attentive that there is not a third act in Calabria.”

The multiple killings stunned Duisburg, a sooty industrial city on the Rhine that has long been a magnet for Italian immigrants. They had come by the thousands after World War II to work in its factories and steel mills.

Italy’s deputy police director, Luigi de Sena, told the ANSA news agency that the slayings were an “unprecedented settling of scores” because they “took place in a foreign country for the first time.”

But crime experts here said ’Ndrangheta had been active in Germany for many years, in part because of the country’s large Italian immigrant population.

Until now, though, the group has kept a low profile, without such public acts of violence. “The police basically ignored them,” said Andreas Ulrich, a reporter at the news magazine Der Spiegel, who has written a book about the ’Ndrangheta in Germany.

There are 530,000 Italian immigrants in Germany, the second largest group after Turkish immigrants, and they are generally viewed as being better integrated into German society.

The German police said the six victims were from San Luca, a small town in eastern Calabria, a rugged, poor province that forms the toe of the Italian peninsula, south of Naples. Two of them were brothers.

On Tuesday night, the police said, the men celebrated the 18th birthday of one of the victims at the pizzeria, Da Bruno, where all six either worked or had an ownership interest. Shortly after 2 a.m., a woman walking nearby heard gunshots and flagged down a passing police car.

The police said they were looking for two men seen running from the scene around the time of the shootings. They are also examining videotape from surveillance cameras. “There were many shots and shot wounds,” said Heinz Sprenger, the chief investigator in the case.

Mr. Sprenger said four of the victims were in a Volkswagen Golf and the other two were in an Opel van. German television showed images of two bloodied bodies lying on the sidewalk under sheets — one wearing black trousers and shoes, the other in short pants with tan loafers.

The exact details are murky, but the feud between the families — the Strangio-Nirta and the Pelle-Romeo — dates to 1991, when two members of the Strangio-Nirta family were killed, according to Italian news reports.

The cycle of violence flared up again this month, when a man named Antonio Giorgi, 56, was shot to death in the town of Benestare. The Italian authorities suspect one of the victims in Duisburg had been marked by the Pelle-Romeo family as a possible reprisal for that killing.

This person “probably expected something to happen, and it seems that he may have been looking for arms to defend himself,” said Mr. Amato, the interior minister.

The reach of mob violence outside Italy may signal a change for ’Ndrangheta, a confederation of families thought to have come into existence around the time of Italian unification, in 1871. The name is often translated, from Greek, as “virtue,” and it refers to the 100 or so families involved.

While the ’Ndrangheta has historically been less hierarchical than the Sicilian Mafia — bound by family ties rather than rules — the killing may mark an attempt by one family for dominance, said Aldo Pecora, head of an Italian anti-mob group called Kill Us All.

Mr. Pecora said the scale of the killing also seemed aimed at demonstrating — to rival families, to the authorities, to people in Calabria — the family’s will to use violence to achieve its ends.

The group reportedly earns tens of billions of dollars each year, largely from narcotics smuggled from Latin America, but also from extortion and other smuggling.

“It’s a message and a message to Calabria above all,” Mr. Pecora said. “It says: ‘Pay attention. We will do what we want.’ ”