Four Palestinians have been killed and there have also been a number of Israeli casualties after fighting resumed in Gaza.
The incident happened two hours into the three-day truce between Israel and Hamas which the US and UN says is aimed at “giving innocent civilians a much-needed reprieve from violence”.
Palestinian officials say 15 people were wounded in Israeli tank shelling east of the southern Gaza city of Rafah.
Both sides accused each other of breaching the temporary truce, which began at 8am (6am UK time).
An Israeli government spokesman said artillery was fired in response to a “serious incident” on the border in the Kerem Shalom region.
Israel’s ground forces are remaining in place during the truce and will continue to destroy cross-border tunnels it says the Hamas militant group uses to try to launch attacks.
Previous ceasefires have been agreed, although none have so far taken hold.
Gazans will receive humanitarian relief and be able to bury the dead, tend to the injured and restock food supplies.
Sky’s David Bowden, reporting from Gaza City, earlier said the truce was having an impact on people in the territory.
He said: “There something about this ceasefire. It’s busy out here this morning. People have got stuff to do that they haven’t been able to do for the last 3-4 weeks because they have been under bombardment.
“Seventy-two hours is a chunk of time to get back to your house, to try to find out whether you have got items you can salvage. It’s a proper window. If it holds, I think people will get a lot done.”
US Secretary Of State John Kerry and UN chief Ban Ki-moon had urged both sides to show restraint before the ceasefire came into force.
However, five Israeli soldiers were killed by mortar fire on the Gaza border on Thursday night, bringing the number of troops killed to 61.
Israeli tank fire left eight Palestinians, including at least two children, dead in Khan Younis.
More than 1,400 Palestinians, most of them civilians, have been killed during the conflict, now in its 25th day.
Delegations from both sides will travel to Cairo, Egypt, immediately to negotiate a more durable deal, with one US official saying talks could start later.
It comes as the US offered its strongest condemnation yet of Israel’s military operation in Gaza.
The White House linked the country to involvement in the shelling of a UN-run school housing more than 3,000 refugees for the first time.
It described the attack, which left 16 people dead, including a number of children, as “totally unacceptable and totally indefensible.”
It was one of several buildings sheltering Palestinians which have come under fire since Israel launched its offensive earlier this month in the face of “persistent” Hamas rocket attacks.
An Israeli Defence Forces spokesman said at least 73 missiles were fired from Gaza on Thursday alone.
A quarter of Gaza’s population, some 440,000 people, have been displaced by the fighting, according to the United Nations.
The head of the UN Relief and Works Agency, Pierre Krahenbuhl, said those in its shelters are facing “dire conditions” as a result of the “extensive and often disproportionate use of force”.
