Soldiers try to enter the National Assembly building in Seoul on December 4 2024, after South Korea President Yoon Suk Yeol declared martial law. Jung Yeon-je, AFP 

South Korean military officials said martial law will remain in effect until it is lifted by President Yoon Suk Yeol, despite the parliament's overwhelming vote on Wednesday to block it.

The martial law will "remain in place until lifted by the president", Seoul's military officials said, according to local broadcaster YTN and other local media reports.

TIMELINE: South Korea’s Yoon Suk Yeol declares martial law

Yoon on Tuesday declared martial law, accusing the opposition of being "anti-state forces" and saying he was acting to protect the country from "threats" posed by the North.

The National Assembly was later sealed and helicopters were seen landing on the roof, as army chief General Park An-su took charge as martial law commander and immediately issued a decree banning "all political activities".

Troops entered the building for a short time, while hundreds of protesters gathered outside parliament chanting: "arrest Yoon Suk Yeol" and facing off with security forces guarding parliament.

Yoon's stunning announcement -- South Korea's first declaration of martial law in more than 40 years -- came as his party and the opposition bicker over the budget.

With martial law imposed, all military units in the South were ordered to strengthen their emergency alert and readiness postures, Yonhap news agency reported.

Some 190 lawmakers managed to get in to the assembly in the early hours of Wednesday, where they unanimously voted in favour of a motion to block the martial law declaration and call for its lifting.

Under the constitution, martial law must be lifted when a majority in parliament demands it, but it was not immediately clear whether this would be respected.