Tens of thousands of Palestinians were rallying for unity in the centre of Gaza City on Tuesday, a spokesman for the Hamas-run interior ministry told AFP.
"There are tens of thousands of people already there, and there may be more on the way," said Ihab Al-Ghussein.
Palestinian activists across the Gaza Strip and the West Bank are staging a day of massive demonstrations to call for unity between Gaza's Hamas rulers and the Fatah-dominated Palestinian Authority which rules from Ramallah.
Another 3,000 or so demonstrators were holding a parallel rally in Ramallah.
As the sun broke over Gaza City, several hundred Palestinians could be seen massing in the Square of the Unknown Soldier ahead of a sit-in which was expected to start at midday, an AFP correspondent said.
The March 15 protest movement, which was planned through Facebook by young activists demanding an end to the division between the warring Fatah and Hamas factions, is expected to see thousands gather for two major rallies in Ramallah and Gaza City.
Demonstrations began on Monday in the Hamas-governed Gaza Strip, where some 3,000 young people had converged upon the square in a party-like atmosphere to demand reconciliation between Gaza's Hamas rulers and the Fatah-dominated Palestinian Authority in the West Bank.
As darkness fell, many went home, but around 60 people slept the night there in small tents under banners reading "Stop the division" and "Yes to Palestinian national unity," an AFP correspondent said.
Among them were a number of people who on Monday began a hunger strike to demand the two warring factions unite, activists said.
Organiser Hossam Khadra told AFP they had finally received a permit to demonstrate after previously being refused.
"Yesterday the interior ministry told us we have permission to demonstrate until 5:00 pm (1500 GMT)," he said.
"But we don't want anyone from the factions interfering. We are young people who want to end the division. We don't want this demonstration to become political."
In the West Bank city of Ramallah, around 12 protesters slept the night in Manara Square, all of whom have been observing a hunger strike since Sunday.
"We are hunger striking to prove that we exist in the real world and not just online, and to show that we are ready to die to end the division," organiser Fadi Quraan told AFP, while expressing similar concerns about the factions trying to co-opt Tuesday's rallies.