Skirmishes in major Venezuelan cities in recent weeks have culminated in a shoot-out in Caracas at the Central University on 7 November, leaving nine people injured.

The violence follows a series of student-led protests, which have ranged from calm to brutally violent in the run-up to a referendum due to be held on 2 December on President Hugo Chávez's constitutional reforms. Under these, the president can stand for indefinite re-election.

Startling footage from the scene showed masked bikers wielding shotguns, students in gas masks hurling Molotov cocktails through clouds of tear-gas, and general chaos as terrified groups scattered at the piercing cracks of semi-automatic gunfire.

Fighting broke out after students returned from a peaceful march to the Supreme Court, where they had been calling for the referendum to be delayed to allow more time for discussion on the reforms. The courts are unlikely to grant that demand.

What happened next depends on whom you talk to - or which television station you watch.

Globovisión, the only public access channel to remain critical of the government after the forced closure of Radio Caracas TV in April this year, blamed pro-Chávez troublemakers for instigating the violence. It reported that a bus full of students was pulled over, emptied and then torched by "Bolivarian Circles" - Chavista loyalists, who the opposition has branded a "militia" armed by the government, a charge denied by the president.

Globovisión went on to report that the Bolivarians entered the campus on motorbikes and opened fire on students, who retaliated in "self-defence". Venezuelan newspapers, which are generally hostile towards Chávez, reported similar stories.

News channels sympathetic to the government, which now make up the majority of broadcasters, reported that "fascist" students attempted to "lynch" an innocent group of Chavista loyalists holed up in the social studies faculty - the only pro-government stronghold on a campus hostile to Chávez.

Zarida Seijar, a 25-year-old pro-Chávez student who was among those trapped inside the building, maintained that the anti-Chávez protesters were the aggressors. "They were shouting that all Chavistas were going to die; we were terrified. When we realised the police weren't going to come, we started texting our friends who came with guns to save us," she said.

Whatever the precise sequence, it is clear the student movement has become the most powerful and well-co-ordinated resistance group against President Chávez. Born during the closure of Radio Caracas TV and spurred on by the defection of the former defence minister Raú Baduel, the angry students have no single figurehead or well-defined agenda. But their increasing militancy and the strong-arm measures taken to quell them is taking their message of defiance to an international audience.

Speaking to Latin American leaders at a summit held in Chile two days after the protests, Chávez claimed that the students are part of a "fascist offensive" under direct control from Washington. "The United States organised the 2002 coup and now it is doing the same in Caracas, supported by the media and CNN," he said, which was denied by the US embassy in Caracas. Brandishing copies of newspapers portraying his supporters as the instigators of 7 November violence, Chávez insisted: "It's the other way round; it was the rich kids [who where responsible]."

By the time Chávez delivered these words, an eerie calm had descended amid the charred detritus around the campus. But feelings still run high. Those who oppose the reforms - which would grant yet more powers to the executive and president - see this as their final opportunity to thwart Chávez's ambitions before Venezuela undergoes irrevocable change.

"We don't know what we will do after this; it really could be our last chance. These reforms centralise all control," said 19-year-old Veronica Brito. "Universities have always been places where federal politics have been off the table. Under this new constitution, they would lose their autonomy."

Other controversial measures include granting the president direct control over the Central Bank, eliminating freedom of information in "exceptional" circumstances, and a loosening of the state's obligation to adhere to human-rights legislation. Intellectual property would be abolished, monopolies prohibited, and the president would assume the right to appoint regional vice-presidents, reducing elected governors to ceremonial positions. The military would be redefined as an "anti-imperialist popular entity", and the threshold number of signatures necessary to trigger further referenda or elections would be raised across the board.

But support for the proposals remains strong; around 60 per cent according to one newspaper survey - thanks mainly to grass-roots loyalty and the inclusion of popular measures such as a six-hour working day and more welfare support for workers. Significantly, 5 per cent of state revenues will be set aside for a new "popular power" fund to finance projects such as Chávez's much-vaunted communal councils. The councils, expected to total around 50,000 by the end of the year, have been hailed as an innovative mechanism for devolving state power and funding.

Even though the student movement is aiming to ratchet up the pressure with further rallies, Chávez still looks set to maintain his clean sheet of electoral victories. Only a nationwide outburst of mass opposition could interrupt Venezuela's inexorable socialist metamorphosis.