Three others were also injured in the gunfight, which broke out around 10:30 pm (2030 GMT) on Saturday.
The police commissioner and several investigators were on the scene at the foot of a four-storey building where the killings took place.
At least eight people have been shot dead on the streets of Marseilles since the beginning of the year, part of a growing number of gang-related murders in the city.
"It's dramatic and desperate," Samia Ghali, the mayor of the eighth district of the city, told AFP.
"It does not give much hope for future generations. There is real work that needs to be done."
French Interior Minister Bernard Cazeneuve said an investigation had been opened, reiterating "the government's absolute determination to eradicate organised crime".
At least 19 people were murdered in and around Marseilles last year, compared to 18 in 2014 and 17 in 2014, many of which authorities believe were carried out by gangs linked with drug trafficking.
On March 17, a 35-year-old man was killed by two men armed with Kalashnikovs, who ambushed him while driving then gunned him down as he tried to flee.