The zone B of Government Complex as seen in October 2016. (Bangkok Post file photo)

State-owned Dhanarak Asset Development Co is selling bid envelopes for construction of the 81-rai Chaeng Watthana Government Complex's Zone C as part of efforts to ramp up state investment to boost the country's economic growth.

The bid envelope sales will go on until Nov 25, with project construction expected to begin by 2019 and conclude by 2022, said Chakkrit Parapantakul, chairman of Dhanarak Asset Development and director-general of the Treasury Department.

The project's investment value is expected to be 15 billion baht for developing a usable area of at least 400,000 square metres, said Mr Chakkrit.

Borrowing costs for the project are estimated at 3-4%, making it attractive for investment, he said. By contrast, borrowing costs to fund construction of the complex's Zone A and Zone B have been 10-11% over the past 10 years.

When construction of Zone C is completed, the total usable floor area will be enlarged to at least 1.4 million sq m, with parking space accommodating more than 10,000 cars.

Public investment has been the mainstay of economic growth as other engines including domestic consumption, exports and private investment remain lacklustre.

The government also hopes that state investment will rev up private investment, helping the country overcome subpar growth in the long run.

Finance Minister Apisak Tantivorawong said recently that the government aimed to step up state investment by bringing forward state enterprises' investment projects over the next two years to next year.

The move seeks to ward off potential downside risks to growth from increasing global uncertainties amid tepid private investment.

For the traffic jam problem in front of the Government Complex, Mr Apisak voiced confidence that the problem would be alleviated after construction of the Red and Pink Lines is completed, with construction schedules for both routes hewing closely to Zone C's.

Meanwhile, Dhanarak Asset Development president Sumeth Damrongchaitham said Zone C will be developed as a smart building under the concept of natural conservation.

Zone C's floor area ratio will be 4, compared with 2.5 for A and B.

The company is considering fund-raising options to finance investment for the project, Mr Sumeth said.