BEIJING - Amid farmlands on the outskirts of Beijing, a massive construction site rising above the horizon bustles with activity as 8,000 workers build a new mega airport.

Aimed at easing passenger load from Beijing's other two airports, Daxing International Airport is scheduled to become operational in June 2019, said Li Jianhua, vice chairman of Beijing City Planning New Airport Construction.

It will operate at full capacity by 2025 with eight runways expected to transport 72 million passengers annually -- making it set to be the world's busiest airport.

The International Air Transport Association has forecast that by 2020, existing airports in Beijing, Manila and Singapore will have reached full capacity.

"All our projects have finished on time or ahead of schedule and our techniques are all in line with international standards," Li told journalists on Thursday during a site visit. Built at a cost of 63.9 billion yuan ($9.35 billion), the new airport will use some 200,000 tonnes of steel, the same amount used in building China's Liaoning aircraft carrier, Li said.

He added that builders have been working at a rate equivalent to putting up one 18-storey building a day.

Inside the construction site, beams of light shone through the glass roof illuminating the dark insides of the building.

A slew of propaganda posters encouraging occupational health and safety are strung up across the site with a giant Chinese flag hung up in the centre of the building. Some 7.8 billion people are forecast to fly worldwide by 2036 with nearly half of passengers flying to, from, or within Asia Pacific said IATA chief Alexandre de Juniac earlier this year.

Meanwhile, China's major airlines mostly saw their earnings battered in the first half of the year as a weaker Chinese yuan and higher fuel prices offset steadily rising passenger traffic. Net profit at China Eastern Airlines for January-June plunged 48 percent on-year to 2.3 billion yuan ($337 million), the company said in a statement to the Hong Kong stock exchange, where it is listed.

"China's civil aviation industry continued to maintain a rapid, above double-digit growth rate, yet also faced challenges such as a sharp rise in fuel prices, large fluctuations in ... exchange rates and intensifying market competition," the Shanghai-based carrier said.

China Southern Airlines, Asia's largest carrier, said earlier in the week that profit slumped 24 percent to 2.1 billion yuan. However, it said revenue grew 12 percent and it posted similar gains in passenger numbers, the latest in what has become routinely good news in the underlying business of Chinese airlines.

Flag carrier Air China bucked the trend, posting a 4.05 percent profit gain to 3.5 billion yuan.

Air China noted, however, that fast growth in transport capacity may have outpaced demand during the period.

The three government-controlled airlines have ramped up their presence in the booming domestic market after previously expanding overseas routes.

China is now the world's second-largest aviation market, and increasing demand for air travel among its growing middle class is expected to ultimately push it past the United States.

Last year, American Airlines, the world largest carrier by scheduled passengers, bought $200 million worth of China Southern stock, or 8.8 percent of its Hong Kong-listed shares, to seal a planned "long-term relationship".

The tie-up will allow American to tap into the Chinese market, while boosting China Southern's ambitions of raising its global profile.