Most of its systems were restored by Wednesday, but miscellaneous functions remain shaky and disruptions to a wide range of services from payments to taxis and restaurant bookings have raised questions about public reliance on the app.

KakaoTalk, launched in 2010, has more than 47 million active accounts in South Korea, making it one of the most ubiquitous apps in the country of 51.6 million.

Hong, who is also leading the company’s response to the outage, said Kakao would look into why service recovery work was slow, prepare compensation for users and businesses affected by service disruptions and build its own data centres.

“We’ll build our own infrastructure including data centres to ensure our services will not be affected by similar incidents going forward,” Kakao said in a statement.

The company plans to invest 460 billion won (US$325 million) to start operating its own data centre from next year, and another one will be completed in the following year, it said.

More than 500 small businesses complained about lost sales due to the Kakao outage, lobby group Korea Federation of Micro Enterprise said.

“I feel very heavily about the inconvenience and damage that Koreans are experiencing,” Yoon said, according to a statement from the presidential office.

“In addition to identifying the exact cause, measures to prevent accidents – including the installation of twin data centres – and a reporting and action system in case of an accident, should be thoroughly prepared,” he said.

Additional reporting by Agence France-Presse