After a decade of wrangling, South Korea is set to inaugurate a new mini-capital seen by supporters as a developmental triumph and by critics as a classic pork-barrel project.

Sejong City will by 2015 house 16 ministries or agencies and 20 central government offices currently located in or near Seoul. More than 10,000 civil servants will work there when construction is completed.

The stated aim is to rebalance national development, in a country where Seoul and its satellite cities house almost half the population and account for almost half national output.

The new city, 120 kilometres (75 miles) south of Seoul, will formally open Sunday, with an inauguration ceremony Monday to be led by Prime Minister Kim Hwang-Sik.

But some 10 state bodies including the president's office, the foreign ministry, the defence ministry and parliament will stay in Seoul.

Kim himself will commute from Seoul for a while even after his office relocates to Sejong City in September. Critics say the split government will lead to wasted travelling hours and inefficiency.

The new city covers 465 square kilometres (186 square miles). A total of 22.5 trillion won ($19.4 billion) -- including 8.5 trillion won in state funds -- is being spent on infrastructure, government buildings and homes for incoming residents.

The concept of Sejong City -- named after the revered 15th century king who developed Korea's alphabet -- came from Roh Moo-Hyun when he was running for president for the main left-leaning party in 2002.

His stated aim was to ease overcrowding in Seoul by moving the national capital to the central Chungcheong region, traditionally the home of uncommitted voters wooed by both parties during elections.

Roh won the presidency, thanks partly to Chungcheong's support. But in 2004 the constitutional court, acting on a complaint from the conservative opposition, ruled that the capital must stay in Seoul.

Roh modified his plan, keeping some ministries in Seoul and describing Sejong as an administrative city rather than the new capital.

Conservative President Lee Myung-Bak, who took office in 2008, wanted to scale down the project and make it a science, business and education hub instead of a government centre.

But a rebel faction from his own party joined the opposition to derail his plans.

"There are people who have doubts about the city... but the quality of life here will be so much better than in Seoul," JK Oh, a spokesman for the city preparation committee, told AFP.

Housing costs are considerably lower than in Seoul, leaving more money for family and leisure activities, he said.

Sejong City would revive the area's previously moribund economy with a construction boom and new businesses catering to young and highly-educated incoming residents, Oh added.

Construction is in its first stage. The government estimates the city's population -- currently about 120,000 -- will rise to 150,000 by 2015, 300,000 by 2020 and 500,000 by 2030, with its economy expected to grow steadily.

Critics say this is wishful thinking.

The state Board of Audit and Inspection said in February that a lack of private sector investment was likely and the city could miss the 2030 population target.

"Sejong City will be remembered as a colossal disaster, created by populist politicians afraid of saying no," said Cho Dong Keun, an economics professor at Myongji University.

He told AFP the division of ministries between Seoul and Sejong City would entail lengthy travelling time between the two locations, creating inefficiency and slowing decision-making.

Because of the lack of leisure facilities and private cram schools for children in Sejong, Cho said most civil servants would leave their families in Seoul and return home at weekends -- contributing little to the area's economy.

"These politicians kept saying that once a promise, forever a promise," he said. "But sticking to a promise that is dumb, unviable and aimed at wooing voters in election season is worse than breaking one."