Apple has reported another exceptional quarter, nearly doubling its net income and far exceeding analyst estimates on the strength of the seemingly unstoppable iPhone.

However, sales of Apple’s big new product, the iPad tablet computer, came in below expectations. The second version of the tablet launched three weeks before the end of the quarter, and manufacturing constraints prevented Apple from selling more of them.Chief Financial Officer Peter Oppenheimer said progress is being made on expanding iPad production, and the company is expanding the number of countries in which it sells the tablet.

“I’m very confident that we can produce a very large number of iPads for the quarter,” he told investors on a conference call.

Apple said net income for its fiscal second quarter, which ended in March, was $US5.99 billion, or $US6.40 per share, up 95 per cent from $US3.07 billion, or $US3.33 per share, a year ago.

Analysts polled by FactSet were expecting earnings of $US5.37 per share.

Revenue was $US24.7 billion, up 83 per cent from $US13.5 billion a year ago. Analysts were expecting $US23.4 billion.

The results were lifted by the record sale of 18.65 million iPhones, millions more than analysts had expected.

For the current quarter, Apple said it expects revenue of $US23 billion and earnings of about $US5.03 per share. Both figures are below analyst expectations of $US23.9 billion and $US5.26 per share, respectively. Apple commonly lowballs its forecasts, but Oppenheimer said the effects of the earthquake in Japan would lower revenue by $US200 million.