Angry city residents set the fires overnight, which the overburdened fire-fighters struggled to extinguish.
A television team recorded stones being thrown at one fire crew as it attempted to put out a fire in the suburb of Barra.
"They are also attacking us because of the mountains of rubbish in the streets," one fireman said. "It's not the first time they have tried to attack us, and I fear that it will also not be the last."
Rising temperatures have exacerbated the problem of the stinking mounds of trash, which contain up to 5,000 tons of material.
Residents protest new dump
At the height of the crisis in January, there were 7,000 tons of rubbish on the streets of the city of 1 million and the surrounding Campania region.
Neapolitans have reported that the rubbish mountains are hundreds of meters wide in some streets. They have launched protests against the city council's plan to set up a new dump on the outskirts of the city.
Italy's new Prime Minister, Silvio Berlusconi, has said he will treat the rubbish crisis as a priority and will discuss it with his cabinet on Wednesday.
Italy could face hefty fines
The European Commission has threatened to fine Italy millions of euros if it does not sort out the "dramatic refuse crisis."
The rubbish was left lying in the streets for the first time in the spring of last year. The crisis returned at Christmas because there were not enough dumps in which to deposit the rubbish.
The EU's executive arm said that although Italy had set up a commission to deal with the rubbish problem and that this had improved the situation somewhat, the government's measures were insufficient to completely resolve the crisis.