Apple delivered surprisingly strong fiscal third-quarter earnings and signalled that its upcoming 10th-anniversary phone line-up is on schedule, driving the stock up 6% to an all-time high in after-hours trading.

The stock climbed above its intraday record high to $159.10 after the company reported better-than-expected iPhone sales, revenue and earnings per share.

Apple also said it hit a milestone of 1.2 billion iPhones sold.

The April-June quarter is traditionally a soft one for Apple as the market waits for the September launch of new iPhone models.

But last night’s results show iPhone buyers may be less inclined than they once were to delay purchases until a new model is out.

The iPad product lines also showed unexpected strength, service revenue continues to grow at a healthy clip, and even the much-maligned Apple Watch showed a 50% sales increase.

Apple is widely tipped to adopt higher-resolution OLED displays for the latest iPhone, along with better touchscreen technology and wireless charging - which could come with a $1,000 plus price tag.

The phone is expected to launch in September.

The company forecast total revenue of between $49 billion and $52 billion for the current fourth quarter, while analysts on average were expecting $49.21 billion, according to Thomson Reuters.

Apple's fourth quarter generally includes first-weekend sales of the company's latest devices.

The forecast "makes it fairly certain that at least some new iPhone models will be released on the normal schedule," said analyst Jan Dawson of Jackdaw Research.

"That doesn’t necessarily mean all new models will go on sale then, or that they’ll all be in abundant supply, but I would think it means that at the very least the successors to the current phones will be available."

But Bob O'Donnell, chief analyst at TECHnalysis Research, cautioned that if Apple releases cheaper models before the premium models in its 10th anniversary phone line-up, the cheaper models could dampen sales of more expensive units released closer to the holidays.

The company said iPhone sales rose 1.6% to 41.03m in the third quarter ended 1 July, above analysts' average estimate of 40.7m units, according to FactSet StreetAccount.

Apple sold 40.4m iPhones during the same period last year.

But a lower average iPhone selling price of $606 (€512), well below Wall Street expectations of $621, caused iPhone revenue to come in at $24.8 billion, below expectations of $25.5 billion.

Apple Chief Financial Officer Luca Maestri said the weak price was partly explained by Apple lowering the flow of inventory by 3.3m units, which he said were "entirely at the high end of the range".

Apple reports how many phones it sells to retailers, not how many phones it sells to consumers, what is known as a sell-in basis.

When factoring how many existing "high end" phones the company cleared out of retail inventory, Maestri said average selling prices were higher.

The company's net income rose to $8.72 billion, or $1.67 per share, from $7.80 billion, or $1.42 per share, a year earlier.

Revenue rose to $45.41 billion from $42.36 billion in the quarter, typically the company's weakest, beating expectations of $44.89 billion.