Gaza militants have fired more than 25 mortar shells towards communities in southern Israel, the Israeli military said.
It appears to be the largest single barrage fired since the 2014 Israel-Hamas war.
No-one was hurt and the military said most were intercepted by the Iron Dome defence system.
But the high volume of projectiles came as tensions have been running high along the Israel-Gaza border.
Israeli media reported that one of the shells landed near a nursery school shortly before it opened.
There was no immediate comment on the shelling from Hamas, the militant Islamic group that runs the Gaza Strip.
Hamas has said a boatful of students and medical patients would set sail out of Gaza City’s port on Tuesday, aiming to break 11 years of naval blockade that Egypt and Israel imposed after the militants violently took control of the coastal territory.
The expedition would be a new way of challenging the blockade but also raises the possibility of more confrontation and violence as Israel bars any boats from Gaza reaching farther out than six miles into the Mediterranean Sea.
In southern Israel, angry residents complained about how vulnerable they felt after 15 years of rocket fire threats from neighbouring Gaza, which is likely to put pressure on the government to retaliate harshly.
Adva Klein, a resident of Kibbutz Kfar Aza, said she only got about two hours of sleep because of the frequent incoming fire and the sirens warning of them.
Other residents reported machine gun fire from Gaza as well.
“It’s been a really scary morning,” said Adele Raemer, a resident of Kibbutz Nirim.
Defence minister Avigdor Lieberman said he was convening the top military brass at his Tel Aviv headquarters to discuss the situation.
The border area has been tense in recent weeks as the Palestinians have held mass protests aimed at lifting a blockade imposed by Israel and Egypt after Hamas seized power in 2007.
Israeli fire has killed more than 110 Palestinians, most of them during the Hamas-led protests, which climaxed on May 14.
On Sunday, Israeli shelling killed three Palestinian militants from the smaller Islamic Jihad group after the troops found a bomb planted along the border.
Islamic Jihad vowed retaliation.
On Monday, a tank fired at a Hamas position in the Gaza Strip, killing one man and wounding another, after Israeli troops came under fire on the frontier while apprehending two armed Palestinians.
Hamas has vowed to continue the border rallies.
Israel says it is defending its border as well as its communities nearby.
It accuses Hamas of trying to carry out attacks under the cover of protests.