TOKYO (AP) -- Japan Airlines said it was hit by a cyberattack Thursday, causing delays to more than 20 domestic flights but the carrier said there was no impact on flight safety.

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

The airline said the cyberattack had delayed 24 domestic flights for more than 30 minutes, and the impact could expand later in the day.

The Kyodo News Service reported that the airline told police that it may have been the victim of a distributed denial-of-service, or DDoS attack, in which networks are overwhelmed by data from multiple sources over a short period.

JAL's ticket sales for both domestic and international fights scheduled for departure on Thursday were suspended temporarily.

Chief Cabinet Secretary Yoshimasa Hayashi told a regular news conference Thursday that the transport ministry told JAL to hasten efforts to restore the system and to accommodate affected passengers.

Television footage showed many passengers at Tokyo's Haneda airport held up by the attack that hit the year-end holiday travel season.

Other Japanese airlines, including ANA Holdings, Skymark and Starflyer, were not affected.

Japan's main travel season is just picking up, as offices close from this weekend for the New Year holidays, the biggest celebration of the year, when millions of people travel back to their hometowns from the cities.