As to who boarded the plane from the communist state was unknown, but speculation is growing that it might be flying North Korean leader Kim Jong-un to Singapore, two days ahead of the historic summit with US President Donald Trump in the city-state.

Air China's usual Pyongyang-bound routes run three times during weekdays. There is no known flight to Pyongyang on weekends.

The Boeing 747-4J6 that traveled to North Korea is known to be a private jet used by the Chinese government to carry its high-level officials, including President Xi Jinping.

The website did not specify the destination of the plane. Many government chartered planes are known to keep their routes discreet due to security issues.

No other flights were detected from the North, according to the website.

Kim has a personal Ilyushin-62M jet, a Soviet-era narrow-body aircraft. But observers have predicted he may be seeking a chartered plane from China, its major ally, for safety reasons. He also needs a separate aircraft for his delegation and cargo that will accompany him on the trip.

The website reported late Saturday that another Chinese airplane landed in Singapore after leaving Pyongyang, in what experts and watchers predicted may be North Korea's advanced team for the summit talks. 

Trump and Kim are set to meet in Singapore on Tuesday to try to reach a deal on dismantling the North's nuclear weapons program in exchange for security guarantees.

Trump has left for Singapore from Canada after attending the two-day Group of Seven meeting that ended Saturday. He is expected to land at a military air base in Singapore later in the day. (Yonhap)