Apple has warned that it is exploring alternative memory chip suppliers as “very significant” supply constraints threaten future sales of its flagship devices.

The warning came as shares of the world’s most valuable listed company fell more than five per cent in after-hours trading in the United States after the iPhone, MacBook and iPad maker issued a weaker-than-expected revenue growth forecast.

Chief Executive Tim Cook acknowledged that widely reported shortages of advanced chips have made it difficult for Apple to secure the components needed to meet demand for its products.

“We’re seeing some very significant (supply) constraints currently with limited flexibility in the supply chain to remedy it,” he said, according to SKY news.

Apple projected revenue growth of between nine and 11 per cent for the current quarter compared with the same period last year, falling short of Wall Street’s expectation of a 12 per cent increase, according to data from the London Stock Exchange Group.

The company also forecast iPhone revenue growth in the mid-teens, below analysts’ expectation of 17.6 per cent.

Apple, like much of the technology industry, has been racing to meet strong demand for new devices, particularly those that rely on advanced processors and memory chips.