The heads and bodies of at least five people have been found in a wooden boat thought to have come from North Korea.

The gruesome discovery was made after the small vessel washed up close to the Japanese island of Sado, authorities in the country said.

Two decapitated heads and five bodies were found in the stern of the boat, coastguard official Kei Chinen told news agencies.

But such was the scene that met police, he added, it was not immediately possible to confirm whether the heads belonged to the bodies or were from two other people altogether.

The discovery came after an officer first spotted the wooden boat – which featured Korean numbers and letters – on Friday afternoon.

Kim Jong-un: Power in pictures Show all 20 1 /20 Kim Jong-un: Power in pictures Kim Jong-un: Power in pictures Kim Jong-un rides a horse during snowfall in Mount Paektu in this image released by North Korea's Korean Central News Agency on 16 October 2019 Reuters Kim Jong-un: Power in pictures Kim Jong-un visits the newly built Pyongyang Orphans' Primary School on 2 February 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects a women's company under Unit 5492 of the Korean People's Army in November 2019 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects the test-fire of intercontinental ballistic missile Hwasong-14 at an undisclosed location in July 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un celebrates the successful test-fire of the intercontinental ballistic missile Hwasong-14 at an undisclosed location in July 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects a potato at the Samjiyon Potato Factory in North Korea in October 2018 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un rides a horse through a forest in this image released by North Korea's Korean Central News Agency on 16 October 2019 EPA Kim Jong-un: Power in pictures Kim Jong-un inspects a block of frozen fish at a processing facility in North Korea in November 2018 Reuters Kim Jong-un: Power in pictures Kim Jong-un celebrates the succeful launch of a strategic submarine-launched ballistic missile in August 2016 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un shakes hands with Donald Trump as they meet for the first time at the Capella Hotel on Sentosa island in Singapore in June 2018 Reuters Kim Jong-un: Power in pictures Kim Jong-un and Donald Trump share a glance as they meet in the Demilitarised Zone in Panmunjon, Korea in June 2019 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects mushrooms at Pyongyang Mushroom Farm AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects a super-large multiple rocket launcher ahead of a test in September 2019 Reuters Kim Jong-un: Power in pictures Kim Jong-un inspects an apple farm in South Hwanghae Province in September 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects an apple farm in South Hwanghae Province in September 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects dental wares at a newly built factory in June 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un visits Farm No 1116 in September 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un visits a motor factory in November 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un rides a horse during snowfall in Mount Paektu in this image released by North Korea's Korean Central News Agency on 16 October 2019 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects the Command of the Strategic Force of the Korean People's Army at an undisclosed location in August 2017 AFP/Getty

Officers waited until Saturday before boarding it due to unstable weather.

Investigators are now working to identify the cause of death and understand where the corpses might have come from.

It comes amid heightened tension between North Korea and Japan.

Kim Jong-un’s promise of a “Christmas gift” for US president Donald Trump – widely interpreted to mean he was planning new ballistic missile tests – were met with dismay in neighbouring Japan earlier this month.

On Friday, the Tokyo-based public broadcaster NHK posted a news bulletin that incorrectly reported North Korea had launched a missile that fell into waters east of the Japanese archipelago.