An F-4 fighter jet of Japan's Air Self-Defense Force caught fire shortly before its scheduled departure for a flight drill from a base in eastern Japan on Wednesday, but no one was hurt in the incident as the two pilots escaped safely, the ASDF said.

The plane's landing gear malfunctioned for unknown reasons and the fire then broke out, apparently because fuel leaked from the fuel tank that had touched the ground. The plane was heading for a runway at Hyakuri Air Base in Ibaraki Prefecture, northeast of Tokyo, at around 11:45 a.m.

Black smoke was seen billowing from the aircraft at one point. The fire was extinguished about 20 minutes later, the ASDF said.

"It is a serious problem regarding flight safety," Defense Minister Itsunori Onodera told reporters. He said he had not heard about any similar trouble in the past but that the ASDF will confirm the safety of each of the F-4s before they fly.

The base's premises house Ibaraki Airport, which opened in March 2010. The incident caused no trouble to the airport's operations, according to the prefecture.

The F-4 fighter jets are aging and the Defense Ministry plans to replace them with F-35 stealth fighter jets, which will be deployed from the end of fiscal 2017.