Yoon, 61, takes office at a time of high tensions on the Korean peninsula, with an increasingly belligerent North Korea conducting a record 15 weapons tests since January, including two launches last week.

His conservative administration looks set to usher in a more muscular foreign policy for the world's 10th-largest economy after the dovish approach pursued by outgoing President Moon Jae-in during his five years in office.

After winning a tight race in March by the narrowest margin, the new president vowed to "sternly deal" with the threat posed by Kim Jong Un's regime, while saying he would leave the door to dialogue open.

Under Moon, Seoul pursued a policy of engagement with North Korea, brokering summits between Kim Jong Un and then-US president Donald Trump. But talks collapsed in 2019 and diplomacy has stalled since.

Moon remains personally popular, but public frustration with his administration helped sweep his opponent Yoon to power.

But it won't be an easy ride: Yoon is taking office with some of the lowest approval ratings -- about 41 percent, according to a recent Gallup poll -- of any democratically elected South Korean president.

His plan to relocate the presidential office from the decades-old Blue House has soured public sentiment, as many view the costly move as unnecessary.

But Yoon has blasted the Blue House as a "symbol of imperial power", claiming the relocation will ensure a more democratic presidency.

- Expensive ceremony -

Not much is known about Yoon's inauguration speech, which will be closely parsed for any indication of how he intends to begin his five-year term.

Local reports say Yoon is writing the speech himself and that it will focus on three keywords: freedom, market and fairness.

Around 40,000 people have been invited to attend the inauguration ceremony, which is by far the most expensive event of its kind at 3.3 billion won (US$2.6 million).

US President Joe Biden designated Douglas Emhoff, husband of US Vice President Kamala Harris, to lead an eight-member presidential delegation, the White House said in a statement last week.

Japan and China are also sending high-level representatives, with Yoon saying he wants to mend sometimes fractious relations with regional powers.