Police estimated the numbers attending the rally here at 25,000 despite an earlier warning by Gideon Ezra, the Public Security minister, that no more than 5,000 would be allowed to protest. Mr Ezra had cited a possible Palestinian Qassam rocket attack as a reason for the limit.
The rally and today's planned march to the Gaza settlements is the latest in the increasingly desperate effort to stop Prime Minister Ariel Sharon's plans to start evicting all of Gaza's 8,500 settlers in two weeks if they have not left voluntarily by then.
Mr Ezra had reluctantly overruled police requests to ban the rally in Negev, the Israeli town closest to the Palestinian communities of Gaza.
But Mr Ezra warned that the protesters would be barred from marching to Gaza's main settlement block of Gush Katif from either Sderot or from Ofakim, 15 miles to the south, where tens of thousands of protesters were due to spend the night.
With up to 30,000 soldiers and police deployed in the area to prevent anti-disengagement protesters from marching to Gush Katif, Pinchas Wallerstein of the Yesha Council, the West Bank settlers' umbrella body, denied reports of a deal with police. "We will continue on as planned to Ofakim, where, at night, we will get organised for the continuation, on to Gush Katif," he said.
A settler leader, Avner Shimoni, said: "It is impossible to stop the masses of Israel who have only one goal: to reach Gush Katif and overturn this cruel decree."
Before yesterday's rally started, in a near-carnival atmosphere, Yehezkel Giloni, a pro-settler protester, toured the crowd selling a specially printed Book of Psalms proclaiming: "A Jew does not expel a Jew." Calling on a million Israelis each to recite one chapter of the psalms, Mr Giloni, a former advertising executive from Haifa, said: "The psalms are the only thing which can stop the withdrawal."
At the rally Moshe Arens, a former defence minister, dismissed the government's argument that disengagement from Gaza was needed to prevent the Arab population becoming a majority in territory controlled by Israel, saying that Gaza's main cities had already been vacated by the military. He declared: "Let the Army abandon this mission and do its real mission of fighting terrorism."
At least two rockets were launched from northern Gaza last night. Rescue workers said one that misfired killed a three-year-old Palestinian boy and wounded nine other Palestinians while another landed in an open field outside Sderot.