Pre-dawn skirmishes have erupted between police and supporters of Brazil’s president, Jair Bolsonaro, as rightwing activists tried to force their way towards congress before major pro-government rallies that have put Latin America’s biggest democracy on edge.

Footage published by the Brasilia-based news website Metropoles showed military police using pepper spray to repel a crowd of cheering Bolsonaristas in the early hours of Tuesday.

Officers can be seen wrestling with one demonstrator as the group attempted to break through a police blockade on the avenue leading to congress using lorries draped with Brazil’s yellow and green flag.

Other footage shows a police officer drawing his gun in an attempt to deter the mob and Bolsonaro supporters vowing to storm the supreme court. In one video a Bolsonaro supporter can be heard berating the police for blocking the protesters’ path. “God will make you pay for this. You communists!” she shouts.

Tuesday’s Independence Day protests – called by Brazil’s embattled leader in an apparent attempt to project strength at the worst moment of his presidency since it began in January 2019 – have sent shockwaves through Brazilian society.

Many citizens fear violence as hardline Bolsonaro supporters take to the streets to champion a leader whose ratings have plunged as a result of corruption scandals involving his allies and relatives and his handling of a Covid outbreak that has killed more than 580,000 people.

Others worry that with support of the military Bolsonaro could be poised to attempt a self-coup, by which he would grab dictatorial powers by closing Brazil’s democratic institutions.

Bolsonaro’s supporters were publicly calling for him to do just that on Monday as they gathered in the capital, Brasilia, where the president was expected to address supporters.

On the esplanade of ministries – the heart of Brazilian politics – one demonstrator had parked a truck decorated with a photograph of Bolsonaro making gun signs with his hands and a banner that read: “Bolsonaro call in the armed forces”.

Further down the road, near the foreign ministry, another of the far-right president’s devotees carried a flag calling for the dissolution of the supreme court and congress.

On Saturday, Bolsonaro, who is notorious for his admiration of authoritarian leaders and Brazil’s 1964-85 dictatorship, warned a political “rupture” was on the cards.

“It’s going to be glorious for our nation. Glorious!” said Evilasio Inacio da Silva, a Bolsonaro-supporting carpenter who had driven for two-and-a-half days by motorbike to reach the demo from his home 1,200 miles away in the north-east.

“My arm’s a bit dead … But it’s worth it. Because we’re fighting for our freedom,” said Silva, who was wearing a T-shirt depicting Bolsonaro as the Bruce Willis character John McClane from the film Die Hard.

On the eve of the rallies, there was trepidation at an encampment of about 1,000 indigenous protesters two miles from where the pro-Bolsonaro demos are being held.

“I don’t know if it’s fear, but we feel insecure … that someone might come along at night and do something silly,” said Cristian Arapiun, an indigenous activist from the Amazon state of Para.

“These people are crazy and we have no idea what they might do to us,” said Arapiun, whose group had placed a banner near their cluster of tents reading: “Bolsonaro, begone!”

“The atmosphere is really heavy,” said Braulina Baniwa, an indigenous leader from Brazil’s border region with Colombia and Venezuela who said activists were being urged not to leave the camp.

As well as Tuesday morning’s rally in Brasilia, a second mass gathering is being held in Brazil’s economic capital, Sao Paulo, on Tuesday afternoon. Smaller demonstrations are being held in other towns and cities, while some opposition groups are also planning to march, fuelling fears of clashes between the two sides.

Ruth de Aquino, a columnist for the newspaper O Globo, said she feared Bolsonaro was purposefully trying to spark violence in order to distract from his woeful presidency.

“Many presidents resort to overseas conflicts to boost their popularity. In the absence of external enemies, Bolsonaro is inciting an internal war so Brazil forgets his utter incompetence,” she said.