Ukraine's Oleksandr Usyk beat Britain's Anthony Joshua on a surprise split points decision after 12 hard rounds to retain his WBA, WBO, IBF and IBO world heavyweight boxing belts in Jeddah on Sunday.

The fight in Saudi Arabia was a rematch of one in London in September, which Usyk won on a unanimous decision to take the belts from Joshua, but fought with much more intensity and emotion.

The pressure was on both more than ever, with Usyk this time representing a country fighting for its existence after a Russian invasion while Joshua was battling for his boxing future.

Usyk appeared comfortably ahead as the final bell rang at the King Abdullah Sports City Arena but the American judge awarded the fight 115-113 to Joshua, with the British and Ukrainian judges deciding 115-113 and 116-112 to Usyk.

The victory took the 35-year-old's professional record to 20 fights undefeated while Joshua, 32, suffered the third defeat of his career.

Joshua, who had held aloft the Ukrainian flag with Usyk as they waited for the decision in what seemed an acceptance of defeat, then had an uncharacteristic meltdown after a fight billed as "Rage on the Red Sea."

He took two of the belts, dropping them as he left the ring and headed for the dressing room before turning around and stepping back between the ropes to take the microphone and address the crowd.

"Usyk is one hell of a fighter. That’s just emotion," declared the Briton.

"For this guy to beat me tonight, maybe I could have done better but it shows the levels of hard work he must have put in, so please give him a round of applause as our heavyweight champion of the world.

"I was studying Ukraine and all the champions from your amazing country. I’ve never been there. What’s happening there, I don’t know but it’s not nice ... under those circumstances, he's managed to become champion."

The opening round was tentative, with Joshua's corner calling for him to adjust his rhythm, and the bout continued with Usyk constantly moving and using his jab and body shots to good effect.

Round nine raised the tempo dramatically, with Joshua enjoying his best round before Usyk came back hard in the 10th.

Needing a knockout and running out of time, the taller and heavier Joshua was unable to land the telling blows against an agile and elusive opponent who hit back hard.

At the final bell the two embraced, with the Ukrainian sinking to his knees.