Japanese prime minister Shinzo Abe has resigned due to ill health.
Mr Abe has had ulcerative colitis for years – a long-term condition where the bowel becomes inflamed – and said his health had declined around the middle of last month.
Two recent hospital visits within a week fanned questions on whether he could stay in the job until the end of his term as ruling party leader, and hence, premier, in September 2021.
In a news conference the 65-year-old PM said: “I cannot be prime minister if I cannot make the best decisions for the people. I have decided to step down from my post.
“It is gut-wrenching to have to leave my job before accomplishing my goals.”
His departure marks the end of an unusual era of stability that saw the Japanese leader strike up strong ties with President Donald Trump even as Mr Abe’s ultra-nationalism riled the Koreas and China.
While he pulled Japan out of recession, the economy has been battered anew by the coronavirus pandemic, and Mr Abe has failed to achieve his cherished goal to formally rewrite the US-drafted pacifist constitution because of poor public support.
The resignation will trigger a leadership race in the Liberal Democrat Party (LDP), the winner of which must be formally elected in parliament.
Mr Abe did not give any hints as to who his successor could be but media reports suggest Shigeru Ishiba, a 63-year-old former defence minister and the PM’s arch-rival, could be the favourite.
The new party leader will hold the post for the rest of the PM’s term.
Boris Johnson tweeted his best wishes following Mr Abe’s announcement.
“Shinzo Abe has achieved great things as PM of Japan – for his country and the world,” he wrote.
“Under his stewardship the UK-Japan relationship has gone from strength to strength in trade, defence and our cultural links.
“Thank you for all your years of service and I wish you good health.”
Foreign Secretary Dominic Raab paid tribute to the “great things he has achieved as Japan’s longest serving leader”.
As news of the resignation spread, Japan’s benchmark Nikkei average fell 2.12% to 22,717.02, while the broader Topix shed 1% to 1,599.70.
The selling wiped $ 4.7bn off Tokyo’s $ 5.7trn stock market value, which had more than doubled during Mr Abe’s tenure.
The conservative Mr Abe returned as prime minister for a rare second term in December 2012, pledging to revive growth with his “Abenomics” mix of hyper-easy monetary policy, fiscal spending and reforms.
He also pledged to beef up Japan’s defences and aimed to revise the pacifist constitution.
On Monday, he surpassed a record for longest consecutive tenure as premier set by his great-uncle Eisaku Sato half a century ago.
Mr Abe has acknowledged having ulcerative colitis since he was a teenager and has said the condition was controlled with treatment.
After his hospital visits were reported, top officials from his cabinet and the ruling party said the leader was overworked and badly needed rest.
Mr Abe resigned from his first stint as prime minister in 2007, citing ill-health after a year plagued by scandals in his
cabinet and a huge election loss for his ruling party.
He had since kept his illness in check with medicine that was not previously available.
Analysis: This news comes ahead of an important year for Japan – but what does Mr Abe’s shock departure actually mean?
By Tom Cheshire, Asia correspondent
From 1993 to 2012, there were 13 prime ministers (including Abe, in his year-long first term).
Abe bucked that trend, remarkably. He became the country’s longest-serving prime minister earlier this month.
That stability offered the opportunity to steadily pursue stimulatory reforms for an economy that had been drifting.
Such is his influence, that programme even took his name – Abenomics.
So, his departure will come as a shock – and indeed the rumours of his resignation sent the Nikkei, the Japanese stock index, down.
That may seem surprising given Abe’s final term was going to expire next year anyway.
That year will be important for Japan amid the pandemic – not in terms of dealing with COVID-19 itself, which Japan has handled well, recording only 1,241 deaths at the same time as avoiding lockdowns (although Abe’s administration has still received a lot of criticism) – but more for the postponed 2020 Olympics, scheduled to take place in Tokyo next summer.
Japan is determined to press ahead with the games but researchers in the country have told Sky News they depend on a vaccine being widely available.
A change in leadership may complicate efforts to get the country ready.
Abe may be hoping that by announcing his resignation now, his successor will have enough time to see it over the line.
Longer term, there is one main question: can Abenomics survive without Abe?
The programme was already in some trouble with him in charge. Japan entered a recession before the larger effects of COVID.
If the revolving door starts spinning once more, and no successor is able to match Abe’s sticking power, things might start to drift again.