Israel pounded Gaza with 30 airstrikes after vowing "Hamas will pay a heavy price" for the death of a four-year-old boy from rocket fire.

Medical officials reported at least eight Palestinian deaths as the conflict entered its 47th day.

The bombardment came just hours after an attack on the southern Israeli village of Sdot Negev, in which the four-year-old died.

He suffered fatal wounds after the barrage of mortars landed in a collective farm, known as a kibbutz. Israeli military said 90 rockets were fired into the country overnight.

A mobile intensive care ambulance was sent to the scene and firefighters hosed down vehicles that were set on fire in a car park.

Prime Minister Benjamin Netanyahu said Israel's military would raise the tempo of operations against Hamas in the Gaza Strip "until the goals of Operation Protective Edge are achieved".

It was the first Israeli death since a new round of fighting erupted on Tuesday between Israel and Gaza's Hamas rulers following the collapse of ceasefire talks in Cairo earlier this week.

The boy is the fourth civilian in Israel to be killed in an attack from the coastal territory since the outbreak of conflict on July 8.

Earlier in the day three people were injured by shrapnel, after rocket fired from Gaza hit a synagogue in the city of Ashdod.

Hamas also killed 18 people suspected of being informers for Israel on Friday.

The group said 11 were killed by firing squad at the Gaza City police headquarters following sentencing by courts.

Hamas media then reported that seven more alleged informants had been targeted by masked gunmen near a mosque.

Two of those killed were women, according to the Palestinian Centre for Human Rights, which called for an immediate halt to what it said were "extra-judicial executions".

Israel's intelligence services rely, in part, on informers to pinpoint the whereabouts of Hamas leaders.

So far more than 2,000 Palestinians have been killed in the conflict, which began as Israel sought to destroy a network of tunnels used by Hamas and other militants.

A total of 64 Israeli soldiers have also been killed in the conflict.