Hundreds of demonstrators have broken into Guatemala's Congress and burned part of the building amid growing anger over the approval of a controversial budget that cut educational and health spending.
The building in Guatemala City was empty at the time of the attack, which lasted for about 10 minutes.
About 1,000 protesters were demonstrating outside the Congress building.
"I feel like the future is being stolen from us", Mauricio Ramírez, a 20-year-old university student, said. "We don't see any changes, this can not continue like this", said Mauricio Ramirez, a 20-year-old university student. "Whoever is proven to have participated in these criminal acts will fall under the full weight of the law", Giammattei tweeted.
He said he defends people's right to protest "but neither can we allow people to vandalise public or private property".
The president said he had been meeting with various groups to present changes to the controversial budget.
On Friday, according to the Associated Press, discontent over the 2021 national budget in Guatemala rose in social media, with a call for a large protest emerging on Saturday.
Recent moves by the Supreme Court and the Attorney-General, seen by citizens as attempts to undermine the fight against corruption, have also raised Guatemalans' ire.
They also want President Alejandro Giammattei to resign.
He also suggested vetoing the approved budget, firing government officials and attempting more outreach to various sectors around the country.
A man walks past an office of the Congress building set on fire by demonstrators during a protest demanding the resignation of President Alejandro Giammattei, in Guatemala City, Guatemala November 21, 2020. Mr Castillo said he would not resign alone.
Guatemala's Congress, dominated by conservative pro-government parties, this week approved an nearly US$13 billion (S$17.47 billion) budget, the largest in the country's history.
Another key complaints is that the budget was passed by parliament while the rest of the country was distracted by the after-effects of two damaging storms, Eta and Iota.
On Friday, Vice-President Guillermo Castillo expressed his opposition to the budget and said that both he and Mr Giammattei should step down "for the good of the country".
"It was a devious blow to the people because Guatemala was between natural disasters, there are signs of government corruption, clientelism in the humanitarian aid", Jordan Rodas, the country's human rights prosecutor, said.