Israel pummelled Gaza with artillery fire and air strikes on Friday, killing 13 people including three children
According to the Israel Defense Forces, the airstrikes on Gaza lasted for 40 minutes with 450 missiles being dropped and 150 targets hit in northern Gaza with 160 aircraft flying simultaneously.
The strikes hit what the military described as "terror targets" operated by Gaza's ruling party Hamas.
They included a "training facility, an anti-aircraft missile launcher post, a concrete production plant & terror tunnel infrastructure".
Witnesses and security sources said the strikes hit two militant "training sites" in southern Gaza and another target in central Gaza.
A Hamas spokesman said that despite the Israeli action, "Gaza still fights and doesn't break."
The strikes came hours after militants in the Gaza Strip fired a rocket into southern Israel.
Rocket barrages against southern Israel swiftly followed the 40-minute pre-dawn offensive on the fifth day of the most serious fighting between Israel and Gaza militants since 2014.
Gaza's ruling Hamas group launched the rocket attacks at Jerusalem and Tel Aviv in retaliation for Israeli police clashes with Palestinians near Al-Aqsa Mosque in Jerusalem.
At least 122 people have been killed in Gaza, including 31 children and 20 women, and 900 others wounded, Palestinian medical officials said.
Among eight dead in Israel were a soldier patrolling the Gaza border, six Israeli civilians - including two children - and an Indian worker, Israeli authorities said.
Amid the fighting, Israeli PM Netanyahu said conflict with Hamas in Gaza is "not over yet".
Adding to the panic, a few minutes into Friday morning the Israeli army set a message saying "ground troops are currently attacking in the Gaza Strip", a statement it later clarified to mean troops had not entered the enclave but were firing into it.
Later on Friday, an Israel Defence Force spokesman acknowledged the message might have been misleading, saying "these things can sometimes happen in the midst of a complex operation."
Whether or not a land assault does come, the intensifying exchanges of fire and Israeli army statements have prompted many Gazans to share their anxieties on Facebook and other social media.
Palestinian militants fired more rockets into Israel's commercial heartland on Thursday as Israel kept up a punishing bombing campaign in the Gaza Strip.
Four days of cross-border fighting showed no sign of abating, and Israeli Prime Minister Benjamin Netanyahu said the campaign "will take more time". Israeli officials said Gaza's ruling Hamas group must be dealt a strong deterring blow before any ceasefire.
Amid the airstrikes, Hamas militants fired rocket salvoes at Tel Aviv and surrounding towns with the Iron Dome anti-missile system intercepting many of them. Communities near the Gaza border and the southern desert city of Beersheba were also targeted.
Five Israelis were wounded by a rocket that hit a building near Tel Aviv on Thursday.
Three rockets were also fired from Lebanon towards Israel but landed in the Mediterranean Sea, the military said.
In Gaza, Israeli warplanes struck a six-storey residential building that it said belonged to Hamas. Netanyahu said Israel has struck a total of close to 1,000 militant targets in the territory.
Israeli aircraft also attacked a Hamas intelligence headquarters and four apartments belonging to senior commanders from the group, the military said, adding that the homes were used for planning and directing strikes on Israel.
Brigadier-General Hidai Zilberman, the Israeli military's chief spokesman, said attacks on militants' rocket production and launching sites were "disrupting Hamas' activities", but still not to the point of stopping the barrages.
Zilberman said Israel was "building up forces on the Gaza border", a deployment that has raised speculation about a possible ground invasion, a move that would recall similar incursions during Israel-Gaza wars in 2014 and in 2009.
School is in recess in Gaza, and classes have also been suspended in many parts of Israel, including in one town where an empty school was hit by a rocket on Tuesday.
The hostilities have fuelled tension between Israeli Jews and the country's 21% Arab minority who live alongside them in some communities.
Jewish and Arab groups attacked people and damaged shops, hotels and cars overnight. In Bat Yam, south of Tel Aviv, dozens of Jews beat and kicked a man thought to be an Arab as he lay on the ground.
Although the latest unrest in Jerusalem was the immediate trigger for hostilities, Palestinians are frustrated by setbacks to their aspirations for an independent state in recent years, including Washington's recognition of disputed Jerusalem as Israel's capital.
On the Israeli political front, Netanyahu's chances to remain in power after an inconclusive March 23 election appeared to improve significantly after his main rival, centrist Yair Lapid, suffered a major setback in efforts to form a government.