Organisers said they expected this year's anniversary rally to be a unique event commemorating the foundation of Hamas.
"The Palestinian people's trust in the Islamic Resistance Movement, Hamas, increases day by day," Abu Talha, head of popular activities in Hamas, told the Reuters news agency.
"Through this large participation we expect the numbers to be significant this year, during the commemoration of the foundation, God willing," he said.
Sherine Tadros, Al Jazeera's correspondent in Gaza said it was "incredibly important" for Hamas that significant numbers turn up at the rally, with ongoing hardships in the strip threatening to affect the movement's popularity.
"People have come here today and they are still supporting Hamas' control over Gaza," she said.
The celebrations are taking place as Gaza continues to struggle with poverty and attempts to recover from Israel's war on the territory earlier in the year.
Hamas has been unable to rebuild homes, sewage lines and water pipes destroyed in the offensive because Israel and Egypt continue to enforce a border blockade.
Basic goods, such as food and some medicines are allowed into Gaza, but construction materials are not.
Israel first sealed Gaza in June 2006 after fighters captured Gilad Schalit, an Israeli soldier.
It was tightened a year later, when Hamas took control of the coastal strip, ousting forces loyal to Western-backed Mahmoud Abbas, the Palestinian president.
Hamas, an offshoot of the Muslim Brotherhood, was formed in 1987 at the beginning of the first intifada against Israel's occupation in the West Bank and Gaza.
The group, which has carried out dozens of suicide bombings since the 1990s, is considered a terrorist group by Israel, the US and European Union.
The group aims to establish an Islamic state in the region and does not recognise Israel's right to exist.
It has also opposed plans by Mahmoud Abbas, the Palestinian president, to seek a permanent deal with Israel.