As of Sunday afternoon, the top downloads on Apple's app store are alternatives for Kakao's most popular apps. (Lee Yoon-seo/The Korea Herald)

The longest-ever server outage for KakaoTalk, the nation's most popular messenger app, and its affiliated services, is prompting people here to seek alternatives, according to data on Sunday.

As of 3 p.m. Sunday, the top downloads on Apple's app store were alternatives for Kakao's popular apps.

Naver's messaging app Line topped the list, rising six steps since Saturday, while taxi reservation app UT came in second, with GPS location service Naver Map coming in third.

Other mobility apps, such as T Map, Tada, Tmoney Onda and i.M also made their way up the ranks.

The change in the top rankings, which are determined by the number of downloads within a 24-hour period, reflect alternatives sought out by the previously Kakao-reliant users.

Kakao dominates the domestic messenger application market with 94.4 percent market share and nearly 47 million monthly average users in a nation of some 52 million.

It is also the biggest provider of transportation service systems, with 94.63 percent market share in the taxi-hailing market with Kakao T.

However, the services became unavailable for the longest time since the company's launch as on Saturday afternoon, a Kakao data center in Pangyo, Gyeonggi Province, caught fire and caused a server outage that lasted for longer than 11 hours.

Voices regarding the unreliability of Kakao’s services rose up among users with the record-breaking service malfunction.

“Even small companies have spare servers in case of emergencies. I don’t understand why the company’s not doing anything about its continued service failures,” said Lee Na-hyun, a college student. "I would rather use a different messenger."

According to the Ministry of Science and ICT, Kakao has experienced 19 service failures over the past five years. In the case of KakaoTalk, a total of four failures -- including QR check-in and gift-giving services -- have occurred this year alone, with data showing that the messaging app has malfunctioned once every two to three months.