More than 100,000 marchers flooded the streets of Caracas yesterday to protest against proposed constitutional changes that would dramatically widen the powers of President Hugo Chavez.

As polls predicted an agonisingly close result in Sunday’s referendum, legions of protesters stormed along the Venezuelan capital’s central avenue, blowing whistles, waving placards and shouting “Not like this!”

Some taunted "Shut up!" echoing a outburst by King Juan Carlos of Spain at a recent summit, which has become a popular ring tone among students.

There were no official counts of those present but Leopoldo Lopez, an opposition politician, estimated that at least 160,000 had taken part in the demonstration, the official close of the campaign against the proposed reforms.

But Mr Chavez vowed that a march by his supporters, scheduled for today, would see Thursday’s turnout tripled. He has described his fresh-faced rivals as “daddy’s little children”, “fascists; and “the children of the rich”, accusing them of acting on orders from the US Government.

The students who have re-energised the country’s fractured opposition – and at times clashed violently with police – helped to make the rally one of the largest to denounce Mr Chavez since he was elected by a landslide in 1998.

Their movement has been gathering momentum since May, when thousands of undergraduates took to the streets in protest at Mr Chavez’s refusal to renew the license for Radio Caracas Television, a private TV network which regularly criticises government policy.

Now the most potent resistance to his rule, various leaders, with ages ranging from 20 to 26 years, make frequent television appearances and have spoken before the nation’s Congress and Supreme Court.

Demonstrations for and against the reforms have surged across the country in recent months. Polls say that 46 per cent of voters currently oppose the measures, while 45 per cent are in favour.

On Wednesday violence erupted in the capital as hundreds of student protesters lobbed stones at police and members of the Venezuelan National Guard, who responded with water cannons and tear gas.

The president, who is to mount his own push for a “yes vote” by speaking at today’s rally, also counts supporters among university ranks.

Some students are particular fans of a measure that would give students and university workers the power to choose school administrators by direct vote, a move that Mr Chavez says will “take out the embedded elites who took over many of our universities.”

Sunday’s vote – on reforms that would substantially boost Mr Chavez’s presidential authority and extend his mandate – promises to be the closest the leader has seen in nine years of office.

Regarded by opponents as a dictatorial demagogue with dangerous ties to Fidel Castro, Mr Chavez has nevertheless won a succession of elections and referendums on his leadership by a clear margin, largely by appealing to an impoverished majority who have benefited from a raft of social programmes and redistribution of oil wealth previously confined to a powerful elite.

However even among the poor, many of whom revere Mr Chavez as a saviour, there is scepticism over his latest reforms, which would not only abolish term limits and lengthen mandates but allow for media censorship in times of “emergency” and create forms of communal property.

But Mr Chavez insists the changes, which are packaged with sweeteners such as a reduction in working hours and a boost for social welfare programmes, are necessary to give the people a greater voice in government.

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