"To safeguard a liberal South Korea from the threats posed by North Korea's communist forces and to eliminate anti-state elements plundering people's freedom and happiness, I hereby declare emergency martial law," Yoon said in a live televised address to the nation.

"With no regard for the livelihoods of the people, the opposition party has paralysed governance solely for the sake of impeachments, special investigations, and shielding their leader from justice," he added.

The move comes as Yoon's People Power Party and the main opposition Democratic Party continue to wrangle over next year's budget bill.

Last week, opposition MPs approved a significantly downsized budget plan through a parliamentary committee.

The opposition has slashed approximately 4.1 trillion won ($2.8 billion) from Yoon's proposed 677 trillion won budget plan, cutting the government's reserve fund and activity budgets for Yoon's office, the prosecution, police, and the state audit agency, Yonhap news agency reported.

"Our National Assembly has become a haven for criminals, a den of legislative dictatorship that seeks to paralyse the judicial and administrative systems and overturn our liberal democratic order," Yoon said in his address.

Yoon, a former prosecutor, alleged that opposition MPS have cut "all key budgets essential to the nation's core functions, such as combatting drug crimes and maintaining public security... turning the country into a drug haven and a state of public safety chaos."

The president also called the opposition, which holds a majority in the 300-member parliament, "anti-state forces intent on overthrowing the regime".

Yoon justified the imposition of martial law as "inevitable to guarantee the continuity of a liberal South Korea," adding that it would not impact the country's foreign policy.

"I will restore the country to normalcy by getting rid of anti-state forces as soon as possible," he said.

He described the current situation as South Korea "on the verge of collapse, with the National Assembly acting as a monster intent on bringing down liberal democracy".

With martial law imposed, all military units in the South, which remains technically at war with the nuclear-armed North, have been ordered to strengthen their emergency alert and readiness postures, Yonhap news agency reported.

The entrance to the National Assembly has been sealed, and MPs have been barred from entering the building, according to Yonhap.

The imposition of emergency martial law comes as Yoon's approval rating dropped to 19 percent in the latest Gallup poll last week, with many expressing dissatisfaction over his handling of the economy and controversies involving his wife, Kim Keon Hee.