The visit by Sheik Hamad bin Khalifa Al Thani comes over the deep reservations of the Palestinian president, Mahmoud Abbas. Hamas ousted Abbas' forces in Gaza during its June 2007 takeover of the territory, leaving the president in control only of the West Bank.
In a phone conversation on the eve of the visit, Abbas welcomed the emir's intentions to help the people of Gaza, under an Israeli-led blockade since the Hamas takeover, but reminded the Qatari leader that he remains the internationally recognized leader of the Palestinians.
"He stressed the necessity to preserve the legitimate representation of the Palestinian people ... and he asked him to urge Hamas in Gaza to go for reconciliation and to end this split," said Abbas' spokesman, Nabil Abu Rdeneh.
Another Abbas aide, Nimr Hamad, used even stronger language. "Such visits give Hamas the impression that the visitors recognize their rule and that would reinforce the split and not help the reconciliation," he said.
On Monday, however, it was clear that the trip was proceeding.
A late night statement from the office of Egypt's President Mohammed Morsi said his country welcomed the emir's visit to Gaza, which it said were part of Egypt's effort "to break the siege on the people" of the territory.
A convoy of some 30 brand new SUVs and minivans, along with several dozen Qatari security men, crossed through the Egyptian border in preparation for the visit.
Streets were decorated with white and maroon Qatari flags and signs thanking the Gulf nation for its support. Hamas' Interior Ministry, which oversees security, said it had a "well prepared plan" to protect the emir, deploying thousands of security men and blocking roads to Gaza City's main soccer stadium, where the Qatari leader was expected to address a packed audience.
"No doubt the visit is very important. I hope, as many others do, that he will work again to achieve the national reconciliation," said Ihad Awad, a 29-year-old civil servant.
Qatar has played a key role in the reconciliation process. Earlier this year, the emir brought together Abbas and Hamas' supreme leader in exile, Khaled Mashaal, to make a deal. Under the arrangement, Abbas was to lead an interim unity government to pave the way for new elections in the Palestinian territories.
That deal, like previous reconciliation attempts, quickly foundered, in large part because of opposition by Gaza's Hamas leaders.
In a statement, Hamas said the emir's arrival had deep significance. "It is the first visit by an Arab leader at this level to Gaza," it said. "This breaks the political isolation of the government and opens the door to break the siege."
When he crosses through the Rafah crossing along Gaza's southern border with Egypt, Sheik Hamad will discover a territory hit hard by war and international isolation. Hamas, whose violent ideology calls for the destruction of Israel, is considered a terrorist group by Israel and the West.
Following the takeover, Israel and Egypt imposed a blockade on Gaza, a crowded seaside strip of land sandwiched between the two countries. The following year, Israel launched a fierce three-week military offensive in response to repeated rocket fire out of Gaza.
The Israeli actions have hit Gaza's economy hard, and much of the damage from the fighting has never been repaired. Still, Hamas remains firmly in control, and momentum seems to be swinging in the group's favor.
Two years ago, Israel was forced to ease the closure under heavy international criticism after a naval raid killed nine activists trying to break the blockade and sail to Gaza. Then, the Arab Spring swept longtime Egyptian President Hosni Mubarak from power. The election of Mohammed Morsi, a fellow Islamist, in Egyptian presidential elections has raised expectations in Gaza of a new era of warmer relations.
While many Egyptians criticized Mubarak for cooperating with the Israeli blockade, rising militant activity in Egypt's Sinai peninsula have tempered calls for openness with Gaza. Al-Qaida-inspired groups in Sinai are believed to have ties with militants in neighboring Gaza.
Morsi's critics have used his closeness to Hamas to feed fears that Sinai will be controlled by Islamic militants. Morsi's government has backed away from proposals over the summer to establish a free trade zone with Gaza.
Military analyst Hossam Sweilam, a former Egyptian general, said the growing ties between Hamas and Egypt, with Qatar's backing, has "very dangerous ramifications."
Reflecting a fear commonly voiced in Egypt, he predicted Hamas would try to exploit the alliance to move militants into Sinai, potentially drawing Israeli retaliation. Israel captured the Sinai in the 1967 Mideast war, returning it 12 years later in a historic peace deal with Egypt.
"This support will deepen the rift between the Palestinians in West Bank and Gaza Strip and will give a green light to Hamas to move its militant arm to Sinai to use it as its base to launch attacks against Israel and which will give Israel the pretext to invade and occupy Sinai once again," Sweilam said.
The Qataris have said the visit is purely humanitarian. The emir is expected to launch $254 million worth of construction projects, including three roads, a hospital and a new town that will bring thousands of jobs to the impoverished territory.
The economic boost is sure to help Hamas' standing, especially at a time when the rival government in the West Bank struggles to stay afloat because of international donors' failure to deliver promised funding.
The visit reflects the flexible foreign policy that Qatar has taken in recent years.
The oil-rich Gulf state expanded its regional influence during the Arab Spring uprisings that toppled dictators in Libya, Tunisia and Egypt last year, lending support to protesters linked to the region-wide Muslim Brotherhood. Hamas is an offshoot of the Brotherhood, but has adopted a more militant ideology as part of its conflict with Israel.
At the same time, Qatar keeps close ties with Washington, hosting a major U.S. air base and thousands of American troops. The country is leading Arab calls to aid Syrian forces trying to topple Bashar Assad. Yet it also has close ties with Syria's key ally, Iran.
In 1996, Qatar made a groundbreaking move to allow Israel to open a trade office in the capital Doha. The office was closed in January 2009 after Israel's incursion into Gaza, and Qatar then began to boost aid to Hamas.
Qatar already wielded considerable indirect influence through broadcaster Al-Jazeera, whose launch in 1996 was bankrolled by the Qatari government. It also won the right to host the 2022 World Cup, defeating far bigger bidders including the United States and Japan.
Qatar's economic reach goes well beyond its oil and gas riches. Its government-backed sovereign funds hold a variety of trophy assets including stakes in London's Heathrow, Stansted and other British airports; the Italian fashion house Valentino; Britain's venerable Harrods department store; French luxury conglomerate LVMH Moet Hennessy Louis Vuitton and high-end American jeweler Tiffany.
Maggie Michael in Cairo, Mohammed Daraghmeh in Ramallah, West Bank, and Brian Murphy in Dubai contributed to this report.
In June 2007, Hamas ousted Palestinian President Mahmoud Abbas' forces in the Gaza territory. Abbas remains in control of the West Bank.