Mr Chali speaking at Shrewbury International School. His company invested 2.6 billion baht to construct a new city-centre primary campus for the school last year.

Cautious property developer City Realty Co, owned by Chali Sophonpanich, plans to brush up a vacant eight-rai plot on Wireless Road to co-develop a luxury project with Hong Kong-based developer HKR International Ltd (HKRI).

One of the key drivers of the plan is the higher potential of the location after TCC Group, owned by billionaire Charoen Sirivadhanabhakdi, announced a 120-billion-baht investment to develop an upscale mixed-use project at the corner of Wireless and Rama IV roads.

"On Wireless Road, freehold land [feasible for new property development] is very limited, while property prices continue growing," said Mr Chali. "New developments on this road are only luxury projects."

TCC will develop One Bangkok on a leasehold 104-rai plot that will comprise five Grade A office towers, five luxury hotels with around 1,000 rooms, three ultra-luxury residential towers and retail space.

According to sources in the property industry, two of the five luxury hotels will be managed by The Ritz-Carlton, a luxury hotel brand of Marriott International; and Andaz, a luxury boutique hotel brand owned by Hyatt Hotels Corporation.

With the launch of Sansiri Plc's super-luxury condominium project 98 Wireless, Wireless Road has become the most expensive street in Bangkok, with the project recording a new high of 800,000 baht per square metre last month.

"With experience and know-how in luxury development and hospitality, HKRI can help us develop an ultra-luxury project on the plot," said Mr Chali.

The Hong Kong-listed developer has invested in and developed many high-end projects and operated luxury hotels and serviced apartments in Hong Kong, China, Japan, Singapore and Thailand.

In Thailand, HKRI owns and operates The Sukhothai Bangkok, a luxury hotel on Sathon Road. It also developed The Sukhothai Residences, a super-luxury condominium next to the hotel, which was completed in 2011 with the record-high price at the time of over 300,000 baht per sq m.

According to a source in the property sector, HKRI plans to launch a new luxury residential project on a 24-rai plot on Rama III Road by the Chao Phraya River by year-end.

HKRI bought the plot in late 2015 for 2.8 billion baht.

HKRI reported in an interim report 2017-18 (for the period ending on Sept 30, 2017) that it had two future projects in Bangkok.

One is the Rama III Road project, where it will develop 1,500 residential units with construction starting this year.

The other is the Wireless Road project on the eight-rai freehold plot on Wireless Road, opposite Lumpini Park and near the Sarasin intersection, for which HKRI owns 49%.

The remaining 51% is held by City Realty, which it acquired over 20 years ago. In 2010 City Realty sold a 49% ownership stake to HKRI.

"With limited supply, I estimate land prices for a freehold plot on Wireless Road can rise to 2.5 million baht per sq wah," said Mr Chali.

Holding the plot for several years has also proven fruitful. That plot, among many others, benefited from a 2012 change in Bangkok's regulations for locations surrounding Benjakitti Park, allowing for the development of taller buildings.

Apart from timing, the land and buildings tax, which will likely be effective within the next 12 months, is likely another reason driving City Realty to consider a development plan for the plot.

As of December 2017, the National Legislative Assembly's standing committee has outlined the tax rate for vacant plots at 1.2% of appraised prices, with a rise of 0.3% every three years, and a ceiling cap of 3%.

Appraised prices of land on Wireless Road for 2016-19 range from 500,000-750,000 baht per sq w, according to the Treasury Department.

For the plot on Wireless Road, the appraised price is 560,000 baht per sq w, which translates to a tax of 21.5 million baht per year.

But the development plan for the Wireless Road plot may not manifest soon, as City Realty has been treading cautiously since the 1997 financial crisis.

Last year it invested 2.6 billion baht to build a new city-centre primary school campus for Shrewsbury International School Bangkok on a 15-rai plot on Rama IX Road after the first campus on Charoen Krung Road has consistently seen an oversupply of students applying since 2015.

City Realty also plans to develop eight-storey apartments, mainly for teachers to rent, with 300 units worth 1 billion baht on a six-rai plot next to the new campus.

The firm also has a 25-rai plot for future development on Rama IX Road.

Scheduled to open in August this year, the new campus will support 640 pupils aged 3-11. The first campus on Charoen Krung Road for 1,700 students opened 15 years ago with an investment of 2 billion baht.

Mr Chali said the company has three property businesses comprising rental offices, rental apartments and hotels, and industrial estates.

The rental offices include Sathorn City Tower and Asia Center Building on Sathon Road and Emporium Tower on Sukhumvit Road.

Apartments and hotels include the 416-room Bangkok Garden, which the company plans to renovate, Chatrium Hotel in Bangkok and Yangon and Emporium Suites by Chatrium.

The average occupancy rate for the apartments and hotels was 80%, with a 5% increase in annual revenue.