Mobile messaging apps Line and Kakao Talk are busy trying to conquer overseas markets such as Southeast Asia and India. But they may do well to keep a close eye on their home turf of Japan and South Korea as China's WeChat amasses more users.

Among six messaging apps, WeChat saw the biggest upptick in usage in Japan and South Korea last month versus a year earlier, boosted by its gaming, e-commerce and multimedia capabilities, according to data on Android smartphones tracked by Mobidia. An analysis by the mobile analytics firm compared the amount of time users spent on Tencent's WeChat, Naver's Line, Daum Kakao's Kakao Talk, Blackberry Messenger and Facebook's WhatsApp and Facebook Messenger.

WeChat's inroads in Japan and South Korea could help ease some investor anxiety over Tencent's overseas expansion after the Chinese company said it had not gained as large a footprint in Western markets as in other countries. Competition is rife, particularly in tech-savvy Asia, as messaging apps fight to stand out by combining messaging functions with other offerings ranging from cartoon stickers to online shopping. Line said this month it is launching its "Cheap Sure Sure" online grocery delivery service in Thailand, its No.2 market after Japan.

The biggest battlegrounds in the Asia-Pacific are China, Australia and Indonesia, though India is garnering more attention as the local cost of smartphones falls, middle class wealth increases and wireless infrastructure improves. India is the fastest-growing market in the region, the Mobidia data shows, led by WhatsApp, and with Kakao Talk not too far behind at No.2. 

And there will be casualties. Last month, Facebook Messenger usage plummeted in nine out of 10 Asia-Pacific countries, the Mobidia data shows. Samsung Electronics, which once held lofty ambitions for ChatON, said it will discontinue the app in all markets on March 31.