The ministry lowered its 2016 economic growth outlook by 0.3 percentage point to 2.8 percent, joining other private institutions that have already made downward revisions of their own growth estimates.
The government's latest growth projection is on par with a forecast made in April by the Bank of Korea, but is slightly higher than the 2.7 percent expansion estimate by the International Monetary Fund.
Last year, the South Korean economy expanded 2.6 percent annually, decelerating from the previous year's 3.3 percent on-year growth.
"Our economy will likely lose momentum in the second half due to sluggish exports and the end of the government-led tax-cut programs," said Lee Ho-seung, a director general at the Ministry of Strategy and Finance.
"The on-going corporate restructuring process will also have a heavy impact on employment, investment and production."
The finance ministry said sluggish exports, one of the country's key economic drivers, are forecast to continue to face a setback in the coming months because of contracted global demand.
The country's exports will likely fall 4.7 percent in 2016 from a year earlier, narrowing from an 8 percent drop in 2015, with imports declining 6 percent on-year, according to the ministry.
The country's current account surplus will contract to $98 billion this year from $105.9 billion last year as imports increased by a wider margin than exports due to rising oil prices, it forecast.
South Korea's outbound shipments fell 6 percent on-year in May, marking a record 17-month losing streak, which also dragged down domestic facility investment and employment, hurting private consumption in the end.
Also, spending at home does not show signs of an uptick. For one, sales of passenger cars jumped 18.9 percent on-year in March on the back of tax benefits, but its growth slowed to 5.8 percent in April. The figure is expected to backtrack in the second half, as the six-month tax program will come to an end this month.
On the production side, industrial output fell 2.8 percent on-year in April, posting negative growth for the second consecutive month and widening its downward pace from March.
Moreover, due to a slowdown in the global economy and the British vote to exit from the EU, or Brexit, financial uncertainties throughout the world have recently heightened to a large extent, probably making consumers and companies tighten their belts down the road, which may further sap demand here.
Also, nationwide corporate restructuring is under way in the most troubled shipbuilding and shipping sectors, with massive layoffs and bankruptcies of subcontracting companies in store.
The ministry forecast some 300,000 people will be newly hired in 2016, down from 340,000 new jobs created a year earlier.
To counter such downside risks, the government said it needs to inject a combined 20 trillion won, including the proposed extra budget, by utilizing tax revenue surpluses and various state-run funds.
"We will map out the supplementary budget without issuing Treasury bonds," Lee said. "We will raise the money by using last year's rolled-over tax revenue and this year's expected tax surplus."
The exact size of the supplementary budget will be determined after more consultations with the parliament, according to the ministry.
Another 10 trillion won will be spent through state-run corporations, such as the Korea Electric Power, it added.
The ministry said the extra money will make it possible for the government to push for expansionary policy measures to achieve the growth goal this year. In the first quarter, the country's 0.5 percent economic growth was largely fueled by fiscal spending.
Meanwhile, the country's ruling party has been urging the government to consider fiscal reinforcement in a way to fuel economic recovery.
But it is uncertain if the proposed supplementary budget will be approved by the parliament as is initially proposed as the ruling party lost its majority in the National Assembly in the April 16 general elections
The ruling Saenuri Party claimed that an extra budget is needed to support the ongoing corporate restructuring. While the opposition parties agreed to the plan in principle, they demanded the government earmark more money for free child care services.
The government's extra budget proposal also chimes in with the Bank of Korea's recent rate cut to fuel an economic recovery.
Early this month, the central bank slashed its policy rate to a record low of 1.25 percent, calling on the government to take similar actions. (Yonhap)