Shinzo Abe has smashed records as Japan's longest-serving prime minister, championing ambitious economic reform while weathering scandals. But he has once again been undone by his health.

After more than seven years in the job, Abe, 65, said Friday he would be stepping down because of a recurrence of the ulcerative colitis that forced him from office during his first stint as premier.

He had been due to stay on until September 2021, when his party presidency terms ends, giving him an opportunity to see out one final event in his historic tenure -- the postponed Tokyo 2020 Olympics Games.

A sprightly 52 years old when he first became prime minister in 2006, Abe was the youngest person ever to occupy the job, and was seen as a symbol of change and youth.

But in a country that sets much store by tradition, he also brought the pedigree of a third-generation politician groomed from birth by an elite, conservative family.

His first term was turbulent; shot through with scandals and discord, and capped by an abrupt resignation that made him the latest in a succession of short-lived Japanese prime ministers.

After initially suggesting he was stepping down for political reasons, he subsequently acknowledged he was suffering an ailment later diagnosed as ulcerative colitis.

The debilitating bowel condition necessitated months of treatment, but was, he said, eventually overcome with the help of new medication.

The revolving prime ministerial door brought him back to office in 2012 -- and, until Friday, had stayed shut for an unusually long time.

With Japan still staggering from the effects of the 2011 tsunami and subsequent nuclear disaster at Fukushima -- and with its inexperienced government lashed for flip-flopping and incompetence -- the wily veteran offered a seemingly safe pair of hands.

He also had a plan. He called it Abenomics.

The scheme to revive Japan's long-stalled economy -- still the world's third biggest, but more than two decades into stagnation -- involved vast government spending, massive monetary easing and the cutting of red tape.

He also sought to boost the country's flagging birth rate by making workplaces more friendly to parents, particularly mothers, and pushed through controversial consumption tax hikes partially intended to help fund free nursery school places for children, and plug gaps in Japan's overstretched social security system.

Shinzo Abe has developed a canny knack for dodging scandal
Shinzo Abe has developed a canny knack for dodging scandal AFP / Behrouz MEHRI

While there was some progress with reform, the bigger structural problems for the economy never really went away. Abenomics was not enough to right the deflation that has beset Japan for decades, and growth has remained anaemic.

The economy had swung into reverse even before the coronavirus crisis wiped out remaining gains.

Abe's star has waned further in recent months with his pandemic handling criticised as confused and slow, driving his approval ratings down to some of the lowest of his tenure.

On the international stage, he has taken a hard line on North Korea, but sought a peacemaker role between the US and Iran.

He prioritised building a close personal relationship with Donald Trump in a bid to protect Japan's key alliance, despite the US president's "America First" mantra, and tried to heal ties with Russia and China.

But here too the scorecard is mixed: Trump is reportedly still eager to force Japan to pay more for US troops stationed in the country; Tokyo has failed to make progress in resolving the status of northern islands disputed with Russia, and a plan to invite Xi Jinping for a state visit has fallen by the wayside amid growing domestic discontent with Beijing.

And while Abe has not repeated a 2013 visit to a controversial war shrine that sparked regional anger and even a US rebuke, he has pursued a hard line with South Korea over unresolved wartime disputes and continued to float plans to revise the country's pacifist constitution.

Throughout his tenure, he has weathered political storms including cronyism allegations that have dented his approval ratings, but done little to affect his power, in part thanks to the weakness of Japan's political opposition.

But even faced with a paucity of alternatives, many voters have tired of Abe.

Speaking to AFP on the streets of Tokyo, Tetsuya Daimon lamented a litany of scandals, and said it was time for Abe to go.

"He has been in the prime minister's office way too long," said Daimon.

"I don't want to see his face, honestly. Seven years and eight months, too long!"