The telecoms firm turned investment behemoth has poured money into some of Silicon Valley's biggest names and hottest new ventures from AI to biotech through its $100-billion Vision Fund.

People moving their lives online during pandemic lockdowns boosted the tech sector and helped the firm score a net profit of 4.99 trillion yen ($45.8 billion) for the year to March, SoftBank said.

The yearly figure tops Japan's previous record held by Toyota and places SoftBank among the world's most profitable companies.

But the firm warned that virus uncertainties meant there was "no guarantee that the current positive impact will be sustained", while analysts said a recent rout in tech shares could spell trouble for the firm.

In 2019-20, SoftBank reported a net loss of 961.6 billion yen -- its worst ever -- as the start of the pandemic compounded woes caused by its investment in troubled office-sharing start-up WeWork.

But it quickly returned to profit as the impact of Covid-19 lockdowns worked largely in its favour.

As people flocked to shop online, South Korean e-commerce giant Coupang, backed by SoftBank, raised more than $4 billion in its initial public offering (IPO) in March.

The value of the Vision Fund's stake in US food delivery app DoorDash also rose massively following its December IPO.

SoftBank founder Masayoshi Son took a typically defensive tone over the huge annual profit, saying it did not mean investors were "throwing their arms up in the air and giving all the praise".

"We must continue to make profit consistently to prove that all this is not out of luck... in the future, the stock market will go up and down," he said.

- 'Regrets' -

Son admitted he harboured "regrets" over several past decisions.

"There were investment failures. There was WeWork. There was Greensill. There was Katerra. There were many investing mistakes," he said.

"But what I regret more is that there were wonderful companies and I missed them. If I were playing baseball, it was like missed strikeouts."

Soaring tech shares on Wall Street led to consolidated gains of 7.53 trillion yen on its investments, particularly Vision Fund shares, Softbank said.

Masahiko Ishino, an analyst at Tokai Tokyo Research Institute, said the conglomerate should make hay while the sun shines.

"I don't know if 'it's time to harvest' is the correct phrase -- but it's true that now is a good time to see results after the company's investments three or four years ago," he told AFP ahead of the earnings report.

"A big factor behind (SoftBank's strong results) is the soaring US and global markets. It's a powerful driver, as many of the companies SoftBank has invested in are listed in the United States," he explained.

Kirk Boodry, an analyst at Redex Holdings, said a rout in tech shares seen in recent days could threaten SoftBank's plans to list more portfolio companies.

"For Softbank Group, tech weakness hits on multiple levels," he said, noting that Vision Fund public investments were down nearly $3 billion in the past two days.

SoftBank has invested heavily in ride-hailing platforms worldwide in recent years, from California-based Uber to Didi Chuxing in China, Singapore's Grab and India's Ola.

In January, SoftBank announced the sale of $2 billion worth of stocks in Uber following a surge in the US ride-hailing giant's value, though it still remains the firm's main shareholder.

Last month the Japanese group said it will buy a 40 percent stake in Norwegian robotics company AutoStore, which develops warehouse automation technology, in a deal worth $2.8 billion.

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