Apple's quarterly profit soared to a record $18 billion on the back of booming iPhone sales, especially in China.

The California-based tech giant also announced Tuesday that its highly anticipated Apple Watch wearable devices unveiled last year are on track to begin shipping in April.

"We'd like to thank our customers for an incredible quarter which saw demand for Apple products soar to an all-time high," said chief executive Tim Cook.

Apple posted record revenue of $74.6 billion in the quarter, during which 74.5 million iPhones were sold.

In the same three-month period at the end of 2013, Apple reported profit of $13.1 billion on $57.6 billion in revenue.

Analysts credited freshly released larger screen iPhone 6 models along with a partnership with China Mobile as powering sales.

Sales of iPhones doubled in Greater China, its number two smartphone market, according to chief financial officer Luca Maestri.

Apple chief executive Tim Cook described the excitement around the debut of iPhone 6 models in China as "phenomenal."

"We are a big believer in China," Cook said. "It is an incredible market; I think people there love Apple products."

IPhone sales leapt 44 percent in the United States and doubled in Brazil.

"Demand for iPhone has been staggering, shattering our expectation," Cook said.

About 65 percent of Apple's overall revenue came from sales outside the United States.

Sales of iPads dipped but Apple set new records in the quarter for sales of Macintosh computers and revenue from digital goods bought from its Apple Store.

The iPhone 6 was the most popular Apple smartphone during the quarter, but the 'phablet' style iPhone 6 Plus also "did incredibly well," Cook said.

Cook remained optimistic about the long-term potential for Apple's iPad line.

He noted that the ranks of first-time iPad buyers remain strong China, Britain, the US and elsewhere and that the devices account for the bulk of online activity and shopping seen from tablets.

"I believe that, over the arc of time, the iPad is a great business," Cook said. "I am thinking over the long run."

Apple and others are still trying to tune into the rhythm of the market when it comes to how long people typically own tablets before replacing them.

Cook also noted that large-screen iPhones might be nibbling at one edge of iPad sales and Macintosh computers at another edge.

He was confident that an alliance between Apple and IBM announced last year will lead to iPads becoming more enticing devices for workplaces.

Cook also said Apple is seeing rapid adoption of the Apple Pay mobile financial transactions system, which is synched to the latest generation of iPhone.

Apple Pay is limited to the United States, but the company has been barraged with requests for it from businesses in other countries, according to Cook.

"I think this is the year of Apple Pay," Cook said.

Apple's board of directors declared a cash dividend of 47 cents per share to be paid on February 12.

Apple shares rose more than five percent to $115.33 in after-market trades that followed release of the earnings figures.