ROME, July 7 (Xinhua) -- Eight people, including two children, are missing, after a four-storey residential building partially collapsed in the town of Torre Annunziata near Naples on Friday.

The third and fourth floors of the building collapsed at 6:20 a.m. local time (0420 GMT), while residents were still sleeping, local media reported.

"Torre Annunziata search ongoing with no results. Two firefighters injured. USAR (Urban Search and Rescue) teams on the way," firefighters tweeted shortly after noon, six hours after the collapse.

The missing include a couple with two children aged 8 and 11 years, the wife and 25-year-old son of an architect, a 65-year-old seamstress, and a man who works for the municipality, according to RAI public broadcaster.

So far, the only successful rescue was that of a dog, whose elderly owner escaped unharmed because he had gone out at around 5:00 a.m. local time, RAI reported.

"I saw the building crumble and I heard them screaming for help," a woman who lives across the street told Italian news agency ANSA. "I know everyone in that building. My seamstress lives alone on the second floor."

Torre Annunziata Mayor Vincenzo Ascione said the first two floors were uninhabited and were being renovated, according to ANSA.

Televised images showed firefighters, police, and volunteers digging through the rubble with their bare hands in search of survivors, with rescue dogs sniffing out the area.

Seventy people are taking turns in the search for survivors in the sweltering heat, RAI public broadcaster reported.

It is still unknown what caused the collapse.

Naples prosecutors have opened an investigation in an effort to clarify who may be at fault, ANSA reported. The building's foundations are on a lava outcrop overlooking the Gulf of Naples, and reportedly date back to the 1960s.

The building also overlooks a railway line, where train traffic was interrupted after rubble from the collapse fell on the tracks.