At one point the crowd stretched for nearly two kilometers, with people filling the streets in and around the parliament and the capital's main pedestrian square.

"We have gathered in the streets primarily to express our complete dissatisfaction after years of dictatorship, lawlessness, and corruption," said one demonstrator, Ognjen Djordjevic, a 28-year-old resident from Belgrade.

The movement formed after 15 people were killed when a railway station roof collapsed in the city of Novi Sad in November, igniting long-simmering anger over alleged corruption and lax oversight in construction projects.

After Saturday's rally, the interior ministry said that at least 107,000 people had turned out.

The Public Assembly Archive -- a group that monitors crowd size -- gave a much higher figure. It estimated that between 275,000 to 325,000 people took to the streets.

If that estimate was correct, that would make Saturday's protest one of the largest in Serbia's recent history.

For weeks, student-led protesters have criss-crossed the country, holding rallies in Serbia's major cities.

They have also taken their anti-corruption crusade to the rural areas and small towns that have long been the backbone of Vucic's support.

Their return to Belgrade on Saturday ramped up already compounding pressure on President Aleksandar Vucic's government, with several high-ranking officials, including the prime minister, having resigned in recent months.

Saturday's protest, like the others before it, cut across a wide-spectrum of society, bringing together those aligned with the far left and right. 

Amid scores of Serbian flags, some waved banners calling for environmental protection, while others demanded the return of the former breakaway province of Kosovo. 

Following hours of peaceful protests, police later reported that there had been some "incidents and clashes among some participants" of the protests. 

Around 7:20 p.m., a leading student group called on all protesters to exit the area near the parliament, citing security concerns after bottles and stones were allegedly thrown. 

The reports of scattered incidents came as fears rose over potential clashes with supporters of Vucic's embattled government, who had also gathered in the capital.

In the days leading up to the protest, ultranationalists, and militia members camped out near the parliament and presidency.

Ahead of the protest, layers of riot police earlier fanned out near the encampment and around the parliament.

Late Saturday, President Vucic took to the airways again.

"There were no casualties or serious injuries," Vucic said during the national address.

"I'm proud of the police who ensured security for all participants," he added, saying he believed "99 percent" of students had remained peaceful.

A day earlier, Vucic had struck a defiant tone, saying he would not "let the streets set the rules in this country".

Some analysts had earlier warned that the situation would escalate. 

"We can already see for a few days that the regime is trying to escalate tensions," said political analyst Srdjan Cvijic. 

Government-backed media also broadcasted increasingly inflammatory accusations, saying the students are planning to launch a "coup", with Vucic accusing the demonstrators of organizing "large-scale violence". 

However, the day passed with no major incidents. 

Farmers, students, bikers and other civilians mingled along the main thoroughfares in downtown Belgrade, as a parade of tractors headed toward the parliament as crowds amassed.

Ahead of the main afternoon protest, thousands also stood for 15 minutes of silence beginning at 11:52 a.m. to honor the victims of the Novi Sad tragedy, with the time marking the moment of the roof's collapse. 

The ritual was repeated again in the evening, as a sprawling crowd at a major traffic roundabout waved their illuminated mobile phones in the air. 

"We came for justice," Milica Stojanovic, a student at the Faculty of Biology in Belgrade, told AFP. 

"I hope that after this protest, things will change," she added