South Korea President Lee Jae Myung pledged a "significant improvement" in the security of government administrative systems after a major fire at the national data center crippled online services around the country.

At a meeting with dozens of ministers and senior government officials, Lee expressed concerns over disruptions of shipping, postal and financial services ahead of the Chuseok mid-autumn holidays in October.

Government services such as the issuance of new passports and offering aid for underprivileged people would be also affected, Lee said.

The fire which started on Friday at the National Information Resources Service in the city of Daejeon was extinguished on Saturday.

The center acts as a cloud server for many government services and databases for the heavily wired Asian country, which is a global powerhouse in technology. The center also operates data centers in other locations.

The accident was suspected to have started with an explosion on Friday night of a battery produced by South Korea's LG Energy Solution during maintenance, damaging some servers and forcing the shutdown of hundreds of others.

LG Energy Solution declined to comment, saying the case is under investigation.

Firefighters took out all of the batteries burnt in the servers and sent them to investigators, an official at the safety ministry said at a briefing on Sunday.

Lee didn't forecast how long the disruptions would continue, adding the country will have to launch a so-called "dual system" for data security for emergencies.

"I don't understand why we don't have an emergency plan for this kind of predictable event," he told officials.

He asked ministers to propose new budgets to prevent such accidents and investigate the fire thoroughly.

Officials are seeking to resume operations at 551 of 647 government administrative systems, according to the safety ministry.

They have restored 99% of key security equipment and at least half of network facilities that were affected by the fire, the ministry said.