South Korea's President Yoon Suk Yeol on Tuesday declared emergency martial law, saying the step was necessary to protect the country from "communist forces" amid parliamentary wrangling over a budget bill.

"To safeguard a liberal South Korea from the threats posed by North Korea's communist forces and to eliminate anti-state elements... 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 surprise move comes as Yoon's People Power Party and the main opposition Democratic Party continue to bicker over next year's budget bill. Opposition MPs last week approved a significantly downsized budget plan through a parliamentary committee.

"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.

He accused opposition lawmakers of cutting "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."

Yoon went on to label the opposition, which holds a majority in the 300-member parliament, as "anti-state forces intent on overthrowing the regime" and called his decision "inevitable".

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