BEIRUT, Lebanon, Dec. 1 — The official goal was to overthrow the government, but the atmosphere was bizarrely festive today as hundreds of thousands of Hezbollah supporters poured into the center of Beirut, banging drums, chanting slogans, pressing shoulder to shoulder as they surged past army troops seeking to keep order.

Families with little children, old people and young people all heeded the call of Hezbollah, the Shiite Muslim party and militia, packing buses and cars all over the country. By nighttime, however, only several thousand demonstrators remained, smoking water pipes, playing music and vowing to stay, some in tents, until the Western-backed government falls.

“We are having fun, yes,” said Hussein Hanoum, 27, of Hermel in the Bekaa Valley of eastern Lebanon, as he lay across a sidewalk in the midst of a huge crowd. “We have no work. We have nothing else to do, so we came to overthrow the government.”

The mood was light-hearted, but the impressive turnout underscored the challenge this politically divided and fragile country faces as it confronts its most dangerous political crisis since the end of a 15-year civil war in 1990. The government was holed up in the Grand Serail, an Ottoman-era building on a hill overlooking the demonstrations. The prime minister, Fouad Siniora, said that the people could stay in the streets as long as they like, but neither he nor the other ministers would resign.