Microsoft on Thursday briefly overtook Apple as the world's most valuable company for the first time since 2021 after the iPhone maker's shares made a weak start to the year on growing concerns over demand.

Microsoft's shares have risen sharply since last year, thanks to the early lead the company has taken in generative artificial intelligence through an investment in ChatGPT-maker OpenAI.

Microsoft's stock closed 0.5% higher, giving it a market valuation of $2.859 trillion. It rose as much as 2% during the session and the company was briefly worth $2.903 trillion.

Shares of Apple closed 0.3% lower, giving the company a market capitalization of $2.886 trillion. Microsoft and Apple have jostled for top spot over the years.

"It was inevitable that Microsoft would overtake Apple since Microsoft is growing faster and has more to benefit from the generative AI revolution," said D.A. Davidson analyst Gil Luria.

Microsoft has incorporated OpenAI's technology across its suite of productivity software, a move that helped spark a rebound in its cloud-computing business in the July-September quarter.

Apple, meanwhile, has been grappling with weakening demand, including for the iPhone, its biggest cash cow. Demand in China, a major market, has slumped as the country's economy makes a slow recovery from the pandemic and a resurgent Huawei chips away at its market share.

"China could be a drag on performance over the coming years," brokerage Redburn Atlantic said in a client note on Wednesday, downgrading Apple's shares to "neutral".

At least three of the 41 analysts covering Apple have lowered their ratings since the start of 2024.

Shares of Cupertino, California-based Apple have fallen 3.3% in January as of the last close, compared with a 1.8% rise in Microsoft.

Both stocks are expensive in terms of their share price-to-earnings (PE) ratio, a common method of valuing publicly listed companies.

Apple is trading at a forward PE of 28, well above its average of 19 over the past 10 years, according to LSEG data.

Microsoft is trading around 31 times forward earnings, above its 10-year average of 24.

Shares of Apple, whose market capitalization peaked at $3.081 trillion on Dec. 14, ended last year with a gain of 48%. That was lower than the 57% rise posted by Microsoft.

Microsoft has briefly taken the lead over Apple as the most valuable company a handful of times since 2018, including in 2021 when concerns about COVID-driven supply chain shortages hit the iPhone maker's stock price.

Currently, Wall Street is more positive on Microsoft. The company has no "sell" rating and nearly 90% of the brokerages covering the company recommend buying the stock.

Apple has two "sell" ratings and only two-thirds of the analysts covering the company rate it a "buy".