Illegal immigrants and their allies gathered across the United States today for marches, prayers and demonstrations on a planned national day of economic protest, boycotting work, school and shopping to show their importance to the country and its economy.

Early reports suggested that many of the estimated 12 million illegal immigrants in America were following a call to stay away from work, despite fears among some groups that the protest - dubbed Un Dia Sin Inmigrantes - A Day Without Immigrants - might prove counter-productive.

In one of the early demonstrations, about 1,200 people marched in the rural city of Homestead, home to one Florida’s largest Mexican immigrant populations and many major growers of fruits, vegetables and nursery plants.

Jose Cruz, 23, from El Salvador, said he took off the day from his construction job to attend the rally. "If I lose my job, it’s worth it," said Mr Cruz, who has a temporary work permit that is granted to many Central Americans. "It’s worth losing several jobs to get my papers."

Others were working but buying nothing as part of the economic boycott around the country. Some planned to attend protests during lunch breaks or after work. Church services, candlelight vigils, picnics and human chains also were planned.

"We've unequivocally called on all families to participate in the Great American Boycott and the marches - and that translates into not going to work, not going to school, not shopping and not selling," said Nativo Lopez, president of the Mexican-American Political Association.

Mr Lopez called on residents and businesses which are operating as normal today, to support the rallies, which aim to pressure President Bush and a divided Congress to enact legislation to help illegal immigrants. Organisers of the protests want a nationwide amnesty and eventual citizenship for all.

The protesters also oppose a Bill passed by the Republican-led House of Representatives that would reclassify illegal immigrants as felons, punish those who help them and build a fence along much of the US-Mexican border.

A bipartisan Bill stalled in the Senate would bolster border security, but also provide illegal immigrants a path toward citizenship and a guest-worker programme long favoured by Mr Bush. The President himself has criticised the boycott and a measure to have a Spanish version of the US national anthem, urging immigrants instead to learn English so they can sing the original version of the song.

Today's protests are expected to include events in 72 cities, with the biggest in New York, Chicago and Los Angeles, where police were expecting hundreds of thousands to turn out.

In each of New York City’s five boroughs, thousands of workers were expected to take work breaks shortly after noon to link arms with shoppers, restaurant-goers and other supporters for about 20 minutes.

"This will symbolise the interdependence of all of us, not just immigrants, but all of society," said Chung-Wa Hong, executive director of the New York Immigration Coalition.

Some big businesses were shutting down operations: six of 14 Perdue Farms plants will close; Gallo Wines in Sonoma, California, was giving its 150 employees the day off; Tyson Foods Inc., the world’s largest meat producer, planned to shut five of its nine beef plants and four of six pork plants.

But it was business as usual at Labor Finders, a temporary employment office with several offices in the Denver area. "The people who come in here really can’t afford to take a day off," said a spokesman. "Their daily pay just takes care of their hotel and food."

On the eve of the protest, about 3,000 people rallied for immigrant rights at a park in Lynwood, a heavily Hispanic Los Angeles suburb. Organisers of the demonstration called on residents and businesses to support the boycott.

Antonio Villaraigosa, the Mayor of Los Angeles, urged students to stay in school and advised protesters against waving flags of their native countries. "You should wave the American flag," he said. "It’s the flag of the country that we all are proud of and want to be a part of. Don’t disrespect the traditions of this country."

A rally in Chicago representing the city’s Arab, Asian, black, eastern European and Hispanic communities, along with labour groups and religious leaders, could bring out as many as half a million people, organisers said. They urged immigrant workers to ask for time off and encouraged students to get permission to attend the demonstration.

Activists in Florida said many immigrants were concerned about recent federal raids, in which hundreds of immigrants with criminal backgrounds were rounded up in Florida and throughout the Midwest.

"We’re not officially co-ordinating a work stoppage. We are leaving it up to every individual. We don’t want people to lose a job, but we want to encourage people to stand up for their rights," said Maria Rodriguez, head of the Florida Immigrant Coalition.

In California, a spokeswoman for Arnold Schwarzenegger, the state's Republican governor, said a boycott would "hurt everyone", while Democratic state senators passed a resolution supporting the walkouts.

Opponents of illegal immigration spent the weekend building a fence to symbolise their support of a secure border. About 200 volunteers organised by the Minuteman Civil Defence Corps of California worked on a 6ft barbed-wire fence along a quarter-mile stretch of rugged terrain near the US-Mexico border about 50 miles east of San Diego.

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