Hundreds of people from Gaza streamed into Egypt at the weekend after Cairo permanently opened its border with the Palestinian territory, a significant step in undermining a four-year Israeli blockade that has left the coastal enclave in tatters.

Busloads of Palestinians, most of whom had applied to travel in advance, arrived at the Rafah terminal on Saturday morning, anticipating what they hoped was a new page in their strained relations with Egypt.

"We've been patient for so long," said Yusef Abu Yusef, 48, who said he was heading to Cairo to visit friends and to bring back medicines unavailable in Gaza. "In the past, I would come here, never knowing if they would let me cross or not."

Since the Mubarak regime was swept from power in a popular uprising three months ago, its unpopular pro-Israel policies no longer hold. Signalling the shift in the relationship with Israel and acknowledging popular support for the Palestinians, Egypt's interim rulers have thrown open the border with Gaza, giving the enclave's besieged residents an opening to the world.

For the 1.5 million Palestinians living in Gaza, it is like the opening of a pressure valve. For four years, Israel's land and naval siege aimed at weakening Gaza's Islamist rulers Hamas has prevented Palestinians from leaving Gaza in all but exceptional cases, tearing families apart and preventing escape from the Israeli bombs that flattened hundreds of Gaza homes during Operation Cast Lead two-and-a-half years ago.

"I'm so very, very happy," grinned Ahmed Zaorob, a Palestinian in his early 50s who hasn't left Gaza in 20 years. "I studied in Egypt, and I'm very anxious to see it again." Reaching for the hand of his wife, Rwaida, an Egyptian, he said they were going to Cairo to seek Egyptian citizenship for their two adult sons. "I just hope it will last," said Mrs Zaorob. "This is what all Palestinians are afraid of."

Egyptians have previously allowed entry through Rafah to students, businessmen, and those seeking urgent medical care. But the border was often closed without warning for long periods at a time, leading to lengthy backlogs. In the busy waiting hall of Rafah's terminal, Palestinians waited tensely for officials to call their names, aware that even if Hamas allowed them to pass, the Egyptians could still stop them.

But unlike before, most expected to get through. By the end of the first day, more than 400 people had crossed, while fewer than two dozen hopefuls had been turned back, blacklisted by Egyptian officials because of security concerns.

Indeed, not all benefit from the new rules. Men aged between 18 and 40 will need to obtain Egyptian visas before they can travel, a reflection of Egypt's security concerns that an influx of young Palestinians could prove an unsettling influence in a country reeling in revolutionary turmoil. "We cannot say that all of our problems are solved, but some of them are," said Ghazi Hamad, a senior Hamas official. "We want to reach a point where this is working normally without any restrictions."

It is Israel's borders with Gaza that are much more significant, and these remain largely closed. It is through Israel that the commercial goods are transferred, and those wanting to access medical treatment in Israel or visit family in the West Bank must apply for access from Israel months in advance, except in urgent medical cases, and many are turned down.

"It has been like living in a prison, a time of intense frustration for us," said Yab Assawarka, a 60-year-old Palestinian leaving Gaza for the first time in six years. Many others voice similar sentiments, and eagerly anticipate rare family reunions with relatives in Egypt and elsewhere. For Mohammed Abu Mazen, 39, who is leaving to seek medical care, it is his first-ever journey out of Gaza. Asked if he has plans to go further afield, he said: "First Egypt, then I'll think about it."

The International Committee of the Red Cross has decried Israel's policies as "collective punishment" of Gaza's residents. Until last year, the parameters of the siege were so rigid that Israel forbade the import of some items.

But even an easing of the blockade has failed to eradicate a black market trade that has supplanted legitimate business in Gaza, devastating the economy while enriching Hamas, which collects taxes on goods smuggled through tunnels from Egypt.

Rightist Israeli politicians have slammed Egypt's decision to open its border, saying it will lead to increased smuggling of militants and weapons, although, privately, government aides say as long as it is limited to people, they are not overly worried.

Of more concern to Israel is that the development could bolster the flagging popularity of Hamas, enabling the group to pass off the Egyptian decision as its own political achievement. The opening of the border has been seen as a goodwill gesture from Cairo's new rulers to prove that they are carving out a policy different from that of Hosni Mubarak, the ousted leader who distrusted Hamas, an offshoot of the Muslim Brotherhood outlawed under his rule.

Hamas has also won support by signing a longed-for unity pact with Fatah, the West Bank-based party, ending a four-year rift. The deal gives Mahmoud Abbas, the Palestinian president, a much stronger claim to represent the Palestinian people when he, as expected, seeks United Nations recognition in September of Palestinian statehood. The move was bolstered at the weekend by the Arab League's decision to support it.

Israel has vehemently rejected the unity deal, saying it will never negotiate with Hamas, which it regards as a terrorist group bent on its destruction. Israel has the support of Washington, but European states have adopted a wait-and-see approach.

Hamas officials warned that there was no choice but to accept the militant group if peace is to be achieved. "The international community must engage with Hamas," said a Hamas official. "The policy of isolation will not help, it will not bring security."

Where to leave Gaza

Israel

* Erez is the main passenger terminal on Gaza's northern border with Israel. Foreign journalists and workers for overseas NGOs enter Gaza from here. Some Palestinians also cross here, including those seeking urgent medical care in Israel and businessmen, but obtaining permission to do so can be a lengthy process.

* Karni, Nahal Oz and Sufa are all located on Gaza's eastern border with Israel, and are largely closed, although they do operate occasionally. The Karni terminal was being used to bring in humanitarian supplies until March 2011.

* Situated on Gaza's southernmost border with Israel, Kerem Shalom is the main border crossing through which commercial goods can be transferred in and out of the strip. This has seen increased goods traffic since Israel eased its blockade in the summer of 2010.

Egypt

* Rafah is the only border crossing with Egypt, and until Saturday only a few categories of people – such as students and medical patients – could cross. Egypt has now opened this to visa-free travel with some exclusions.

Sea

* Israel has blockaded Gaza's ports since 2007, and fishermen are only allowed to fish up to three miles from shore.

Israeli gunships patrol the waters, preventing any craft from entering Gaza's waters.