Gaza militants fired several rockets towards Jerusalem and Tel Aviv on Saturday, the army said, with no reports of injuries, as Israel continued to bomb the coastal enclave.

Three of the four Tel Aviv rockets were intercepted by the Iron Dome missile defence system, and the Jerusalem-bound rockets fell short, hitting two West Bank cities.

"Three rockets intercepted above the Tel Aviv metropolitan area. Another rocket hit an open area near Rishon LeTzion," the army said in a statement, after sirens and explosions were heard in Israel's commercial capital.

Hamas, which controls Gaza, warned in advance of the rocket fire.

Shortly after 8:00 pm (1700 GMT) , its armed wing the Ezzedine al-Qassam Brigades issued a statement read aloud in Arabic and Hebrew on Hamas's Al-Aqsa TV, pledging to fire J-80 type rockets at Tel Aviv an hour later.

Afterwards, Hamas television claimed Tel Aviv had turned into a "ghost town" after the threat and that dozens of Israelis were being treated for "panic attacks."

Earlier, "rockets were fired from Gaza at Israel and hit the Judea region," the army said, using Israel's term for the southern West Bank.

"One rocket struck an urban area in Hebron and two other rockets struck the area of Bethlehem," it said, giving no details of any casualties or damage.

Shortly before the rockets hit, air raid sirens sounded in Jerusalem, just a few miles north of Bethlehem, before at least two explosions were heard.

Palestinian security sources told AFP one rocket hit an inhabited area of Hebron, and another struck a house in the nearby village of Sair, to the south.

There were no immediate details on the third rocket.

Militants in the Gaza Strip have fired several rockets at Jerusalem and Tel Aviv since Monday, many of which have been intercepted by the Iron Dome missile defence system.

Rockets from Gaza have also reached as far as Hadera, 116 kilometres (72 miles) north of the besieged Palestinian territory.

Since Israel launched what it dubbed Operation Protective Edge against Gaza on Tuesday, aimed at ending rocket attacks from the Hamas-controlled territory, militants have fired at least 525 mortar rounds and rockets that have struck Israel.

Another 141 rockets were intercepted by Iron Dome, the army says.

Israeli air strikes on the enclave have killed 135 Palestinians, and the mobilisation of 40,000 reservists has been authorised in the event of a ground operation.

Rocket fire from Gaza has caused no Israeli deaths, but has seriously wounded two people.