Palestinian militants have fired more than 200 rockets from the Gaza Strip at Israel, the Israeli army said Tuesday morning.
The success rate of Israel's Iron Dome air defence system is 90 per cent, and around one-third of all rockets fired went down while still in the Gaza Strip, an army spokesman said.
He said the extraordinary amount of rocket fire likely resulted in casualties there.
The Israel Defense Forces (IDF) tweeted in the early hours of Tuesday that groups in Gaza had been firing rockets "non-stop" for ten hours.
The IDF also said a residential building in the city of Ashkelon, in southern Israel north of the Gaza Strip, was hit by a rocket. Six people were injured, according to rescuers.
Israel has fired around 130 rockets at targets in the Gaza Strip so far, and an estimated 15 members of Hamas and the Islamic Jihad group have been killed, the spokesman said.
Combat aircraft and drones carried out the attacks targeting rocket production, storage and training facilities as well as military posts.
Israel also targeted two tunnels, which were completed to varying degrees. The spokesman said the counter-attack was in its early stages.
The conflict between Israelis and Palestinians has escalated in recent days.
At the weekend hundreds were injured in serious clashes at the Jerusalem holy site known as the Temple Mount to Jews and the Noble Sanctuary to Muslims.
The Islamist Hamas movement had issued an ultimatum telling Israel to withdraw settlers and police from the holy site and from the neighbourhood of Sheikh Jarrah in Jerusalem by Monday night.
Shortly after the deadline expired, reports of mass rocket attacks began.
A Hamas spokesman said the rockets were a "message" to Israel and a "response to its crimes and aggressions against the holy city."
The Islamic Jihad group in Gaza has also claimed responsibility. On Monday evening, Palestinian militants began firing rockets at Israel.
Israel then shelled targets in the coastal enclave of Gaza. The Gaza Health Ministry said 22 people were killed, including nine children.
The Israeli army spokesman said they were aware of the report and that it is being examined.
Eight Hamas activists were killed in the strikes, according to the Jerusalem Post.