Thousands of Palestinians have formed a "human chain" in Gaza in protest at Israel's blockade of the territory.
Organisers had hoped up to 50,000 people would make a 40km (25-mile) chain from Rafah to Beit Hanoun, but turnout was well below expectations.
The Israeli army said it had detained about 50 people after a group of youths approached the Erez crossing point and began throwing stones.
Israel tightened the blockade when Hamas seized control of Gaza in June.
Thousands of women and children from all around the Gaza Strip travelled to the main north-south road for Monday's peaceful demonstration.
Schools were closed for the day, and thousands of pupils were taken in buses to participate. Many could be seen with banners stating: "The siege of Gaza will only strengthen us" and "The world has condemned Gaza to death".
The protest's organisers, the pro-Hamas Popular Anti-Siege Committee, had planned to place a person every metre along the 40km-long road from the Rafah crossing on the southern border to the Erez crossing near the northern town of Beit Hanoun.
But with heavy rain in parts of the Strip, reports say only around 5,000 took part.
"This is a peaceful and civilised act to let the people express their rejection of the siege and of collective punishment," the group's leader, Jamal al-Khudari said.
"We are raising a cry to the world for it to act."
The Israeli authorities had feared a repetition of scenes last month when Palestinian militants demolished the fence separating Gaza from Egypt in several places, allowing hundreds of thousands of people to cross the border and obtain much-needed supplies.
Earlier, a joint statement by Israeli Foreign Minister Tzipi Livni and Defence Minister Ehud Barak had said Israel "would ensure the defence of its territory and prevent any violation of its sovereign borders".
An Israeli military spokesman, Col Zeev Sharoni, had said the army would "do everything necessary to prevent people from crossing into Israeli territory".
As the protest began to break up in the early afternoon, a group of youths approached the Erez crossing and started throwing stones and burning tyres, prompting the arrests.
Israeli soldiers at the checkpoint are said to have fired into the air to deter the stone-throwers.
BBC Arab affairs analyst Magdi Abdelhadi says the Palestinians in Gaza appear to have realised that mass action is their best chance of getting the attention of the world and generating more pressure on Israel to ease the blockade.
With Israel refusing, and Hamas and Fatah locked in a power struggle, they want to send a clear message to the outside world that ordinary civilians are paying the price, he says.
In a separate incident, an Israeli child was injured by a rocket fired from Gaza by militants.
Israel says the siege, which has prevented the flow of everything but essential humanitarian supplies, is in response to such attacks.
Some youths threw stones and burned tyres
The blockade of Gaza was imposed after Hamas routed Fatah forces loyal to President Mahmoud Abbas last June and seized control of the Gaza Strip.
On Sunday, two Hamas fighters were killed in Israeli airstrikes near the border in Khan Younis, while another died in northern Gaza, the group said.
Israeli forces also detained 40 Palestinians and said they had discovered five smuggling tunnels along the territory's frontier.