Changi Airport in Singapore.

Singapore's ambitious project to double its air passenger handling capacity by the mid-2020s is set to extend its lead over neighbors like Kuala Lumpur, Bangkok and Jakarta, whose airports are struggling with congestion and construction delays.

Changi, Southeast Asia's biggest and most popular international airport, is keen to seize a greater share of a boom in regional traffic, mindful of competitors' plans to grow into international hubs.