Israel has temporarily shut its crossings with Gaza, after a series of rocket attacks on nearby Israeli towns from the Hamas-run territory.
Gaza receives humanitarian and fuel supplies through Israel
The UN relief agency providing for Palestinian refugees in Gaza said it was unable to deliver humanitarian aid as a result of the closure.
The measure came as a woman was killed and at least 40 people were injured by an Israeli missile in Gaza City.
A separate air strike killed at least one militant, injuring several others.
The militants had just launched rockets into Israel, officials on both sides said.
Ministry building hit
A Palestinian woman was killed and more than 40 people were injured when an Israeli missile struck the Hamas-run interior ministry headquarters in Gaza City on Friday, medical sources say.
The building was vacant, having been severely damaged by an Israeli air strike in July 2006, but was situated in residential neighbourhood.
The interior ministry building in Gaza has been vacant since 2006
A wedding was taking place nearby and many of those hurt were women and children, correspondents say.
Another Israeli air strike targeted a disused Hamas security forces building. No casualties were reported.
In a separate incident, a militant from the al-Aqsa Martyrs Brigades, a group linked to the Fatah faction of Palestinian Authority President Mahmoud Abbas, was also killed by Israeli troops in the West Bank town of Nablus.
Ahmed Senakreh was killed in a gun battle with soldiers who had surrounded a house in the Balata refugee camp where he was hiding.
The Israeli military has intensified operations in Gaza this week, killing at least 32 Palestinians, most of them militants, in air strikes.
Hamas, the militant Islamist group, has fired salvoes of unguided rockets for the first time in months, causing injuries in Israel.
The sharp rise in violence in the Gaza Strip comes after a recent US-led push for progress in peace talks.
Roads dug up
Israeli Defence Minister Ehud Barak took the decision to close Gaza's borders on Thursday evening, prompted by the rocket attacks.
More attacks followed on Friday, with one hitting the Israeli town of Ashkelon. No casualties were reported.
"It's time that Hamas decide to either fight or take care of its population," Shlomo Dror, a spokesman for the Israeli defence ministry, said. "It's unacceptable that people in [the southern Israeli town of] Sderot are living in fear every day and people in Gaza are living life as usual."
Hamas has launched over 100 rockets into Israel in recent days
BBC Jerusalem correspondent Katya Adler says the closure should be seen as a warning by Israel to show what it can do if it decides to put increased pressure on Gaza.
The crossings would normally be closed from Friday afternoon to Sunday morning for the Sabbath. Israeli officials have indicated the decision will be reviewed on Sunday.
But, a spokesman for the United Nations Relief and Works Agency (UNRWA), Christopher Gunness, said it was unable to deliver lorryloads of aid because of the closure.
"Gaza is completely shut down. This will only add to an already dire situation," he said.
Gazans were digging up roads because there was no cement for making graves, he said.
"It is imperative that these crossings are opened so that the dire situation in Gaza does not deteriorate further, inflicting further misery on one-and-a-half million people," he said.
The BBC's Martin Patience, who is at the Erez crossing, says he saw one Palestinian needing urgent medical treatment being allowed out of Gaza.
Two Gazans were allowed to cross into the territory, returning from receiving treatment in Israel, as well as a vehicle belonging to UN children's fund Unicef, our correspondent says.
Gaza receives its fuel and humanitarian supplies through Israel, and the territory has been under an ever-tightening blockade since Hamas took it over by force in June.
Last week, a hopeful US President George W Bush was predicting the recently relaunched peace process could result in a deal within a year.
But on Thursday, the Palestine Liberation Organisation (PLO) headed by Palestinian Authority President Mahmoud Abbas warned of "serious consequences" for the talks if the Israeli strikes continued.