The city of Naples in southern Italy is battling an infestation of large red cockroaches brought on by the unseasonally warm weather and unhygienic conditions, health officials said on Tuesday.

Pest control personnel are spraying sewers with poison around the clock to try and hold off an invasion by the roaches, which can be up to seven centimetres long and thrive in heat, humidity and organic decomposition.

The infestation has reignited a debate about problems with waste disposal in Naples, a mafia-linked sector that has been beset by chronic problems.

Local health agency director Maurizio Scoppa said the hot weather and garbage being left out overnight for early morning pick-up were major factors.

"The problem of managing the sewers and the garbage is one of the causes of this phenomenon," Scoppa told AFP, pointing out that city authorities did not have enough staff to be able to carry out sewer inspections.

Some health experts have warned of a heightened risk of typhoid and hepatitis A but a spokeswoman for city hall dismissed the possibility.

"There is no health risk. There is no emergency situation, this is just a phenomenon that affects only some areas," Maria Bonacci said.

"Other experts reject any danger to the health of inhabitants," she said.

Bonacci said talk of an "invasion" of cockroaches was exaggerated but agreed that their number this summer was significantly higher than previous years.

She blamed the previous city administration for "not cleaning the sewers."

Red cockroaches of the same type as the ones in Naples -- also known in Italian as "cockroach of the ships" -- are common in tropical climates around the world and are spread to port cities by global shipping.