Egypt has temporarily re-opened the Rafah border crossing, the Gaza Strip's main crossing with the outside world.
The two-day opening is to allow people stranded on both sides to cross, and for some Palestinians to enter Egypt to receive medical treatment.
Earlier, Israel again closed its commercial crossings with Gaza after accusing Palestinian militants of firing a rocket on Monday.
A truce between Israel and Hamas which, controls Gaza came into effect in June.
Fifty medical cases were the first allowed out of Gaza, travelling across the border in ambulances.
"I have been here since midnight, and I have cancer. I have my permit for three months, and I keep renewing it and there is no crossing," said a man waiting at the crossing.
"Nobody is taking care of us, neither the president in the West Bank (Palestinian Authority President Mahmoud Abbas) or the president in Gaza (Hamas leader Ismail Haniya)," he said.
On Sunday, Israel had reopened the commercial crossing of Sufa to allow about 70 truckloads of goods to enter Gaza.
The 19 June truce agreement - brokered by Egypt - was aimed at halting rocket attacks in return for Israel's lifting of its blockade on Gaza and has been largely holding.
Hamas has been seeking the permanent reopening of Rafah crossing, the only crossing from Gaza bypassing Israel. However, under a November 2005 deal, Israel can control access to the European officials who monitor it.
In this way Israel has kept the crossing mainly closed since the Hamas takeover of Gaza in June 2007.
Egypt last opened the border on 18 June, but only for Palestinians to return to Gaza after receiving medical treatment.
Israel insists "normal business" cannot resume at Rafah until Hamas releases an Israeli soldier captured two years ago.
Hamas blew up large sections of a border fence in January to allow large numbers of Gazans to stock up on goods they had been deprived of by Israel's blockade.
Permanent opening has been left dependent on the outcome of talks between Hamas, the Palestinian leadership and the European Union.
Satellite photo of the Gaza Strip (2005)The border between Egypt and the Hamas-controlled Gaza Strip has closed again after Palestinians attacked the border. The border opened again on Tuesday, but after Wednesday's events, was once again closed.

Egypt had opened the border to allow people stranded on either side to go across, and to allow Palestinians access to supplies and services such as health care. When Egypt restricted passage to only small groups of people, Palestinians began to grow restless.

There are reports of stones being thrown at Egyptian and Palestinian border guards. Three Palestinians are reported to be injured. To repel the riot, the Egyptians used water-canons to keep crowds at bay. The Egypt-Gaza border is now sealed again.

Hamas militants have previously forced open the Egyptian border in January to allow Palestinians to get essential supplies that have been cut off due to an Israeli blockade. Israel has since allowed supplies to flow into the Gaza Strip as per a ceasefire agreement.