TOKYO — Japan Airlines said it was hit by a cyberattack Thursday, causing delays to more than 20 domestic flights, but the carrier said it was able to stop the onslaught and restore its systems hours later. There was no impact on flight safety, it said.

JAL said the problem started Thursday morning when the company’s network connecting internal and external systems began malfunctioning.

The airline said it was able to identify the cause as an attack intended to overwhelm the network system with massive transmissions of data. Such attacks flood a system or network with traffic until the target cannot respond or crashes.

The attack did not involve a virus or cause any customer data leaks, JAL said. It said that as of late morning, the cyberattack had delayed 24 domestic flights for more than 30 minutes.

Experts have repeatedly raised concerns about the vulnerability of Japan’s cybersecurity, especially as the country steps up its defense capabilities and works more closely with the United States and other partners with much tighter cyber defenses. Japan has taken steps, but experts say more work is needed.

In June, Japan’s space agency said it had suffered a series of cyberattacks since 2023, though sensitive information related to rockets, satellites and defense was not affected.

JAL’s ticket sales for domestic and international fights scheduled for departure Thursday were suspended temporarily but resumed several hours later.

Television footage showed many passengers at Tokyo’s Haneda airport crowded into its terminals as the attack hit the year-end holiday travel season.