North Korea's purported spy satellite has entered orbit, Seoul's military said, but warned it was too early to tell whether Pyongyang's eye in the sky was actually working.

South Korea's Joint Chiefs of Staff said Pyongyang's so-called spy satellite "was assessed to have entered orbit from comprehensive analysis of flight track information and various circumstances", adding that "determining whether the satellite is actually operating will take time".

North Korea said it had succeeded in putting a military spy satellite into orbit, with state media claiming Kim Jong-un was already reviewing images of US military bases in Guam.

The US, South Korea and Japan have criticised the sanctions-busting launch, Pyongyang's third attempt this year to put a satellite into orbit, and the first since Mr Kim met President Vladimir Putin at a Russian cosmodrome in September.

After failed attempts in May and August, the official Korean Central News Agency reported that a rocket had blasted off late yesterday and "accurately put the reconnaissance satellite 'Malligyong-1' on its orbit".

Images in state media showed Mr Kim watching the launch, then smiling and waving, surrounded by white-uniformed scientists and engineers celebrating the satellite's purported success.

The satellite will "formally start its reconnaissance mission from 1 December after finishing seven to ten days' fine-tuning process," KCNA reported, adding that it was already transmitting images.

Mr Kim "watched the aerospace photos of Anderson Air Force Base, Apra Harbor and other major military bases of the US forces taken in the sky above Guam in the Pacific, which were received at 9.21am on 22 November," KCNA said.

South Korea has partially suspended a 2018 military deal with the North in response to the launch, saying it would resume surveillance operations along their border.

Japan said it was still analysing the launch and "at this point is not confirming whether the satellite had entered into an orbit", chief government spokesman Hirokazu Matsuno said.

Speaking at Pyongyang's space launch centre, Mr Kim claimed the development meant the North has "both 'eyes' overlooking a very long distance and a strong 'fist' beating a very long distance," in a possible reference to the country's banned Intercontinental Ballistic Missiles, which it claims could hit the US mainland.

Mr Kim "stressed once again that it is necessary to operate many more reconnaissance satellites" to both increase the country's "military strike means... as well as for self-defence."

China, Pyongyang's longtime treaty ally and main economic benefactor, did not condemn the launch but said the situation was "complex and sensitive," foreign ministry spokesperson Mao Ning told a briefing.

"All parties concerned should remain calm and restrained, look squarely at the crux of the problem, adhere to the general direction of a political settlement, and do more to help ease tensions," she added.

South Korea has been saying for weeks that the nuclear-armed North was in the final stages of preparation for another attempted spy satellite launch.

Seoul's spy agency this month said Pyongyang appeared to have received technical advice from Russia in return for sending at least ten shipments of weapons for Moscow's war in Ukraine.

The North's May attempt failed due to the "abnormal" startup of its second-stage engine, Pyongyang state media said at the time, while the August misfire was attributed to an error in the "emergency blasting system".

Mr Putin suggested in September after his meeting with Mr Kim that his nation could help Pyongyang build satellites.

South Korea and the US have both subsequently accused North Korea of shipping weapons to Russia, with US Secretary of State Antony Blinken warning this month that military ties between North Korea and Russia were "growing and dangerous".

The launch also appears to kick off a space race on the peninsula, experts said, with South Korea planning to launch its first spy satellite via a SpaceX rocket later this month.

"Kim Jong-un demonstrated his will to have an upper hand in military superiority by attempting to launch the first military reconnaissance satellite into orbit before South Korea," said Lim Eul-chul, associate professor at the Institute for Far Eastern Studies, Kyungnam University.

"Of course, it appears that there will be differences in the performance of the satellites."

Successfully putting a spy satellite into orbit would improve North Korea's intelligence-gathering capabilities, particularly over South Korea, and provide crucial data in any military conflict, experts say.