Surveys released today showed the popular iPhone 6 and 6 Plus helped Apple pull to a virtual tie in the fourth quarter with Samsung, which has been the leader for the past three years.

The research firm Strategy Analytics said Apple and Samsung shipped 74.5 million smartphones each in the last three months of 2014 for a market share of just under 20 percent.

A separate survey by IDC analysts said Samsung had a tiny edge over Apple with 75.1 million units sold. Apple "beat everyone's expectations," said Ryan Reith at IDC.

Even more surprising is that Apple managed to increase the average selling price of its phones at a time when many consumers around the world are looking to low-cost handsets.

Another surprise was growth of iPhone sales in the US, "which is considered a saturated market," according to Reith, and in China, where competition is intense.

"Sustaining this growth and higher (selling prices) a year from now could prove challenging, but right now there is no question that Apple is leading the way," Reith said in a statement.

Samsung, which belatedly entered the market pioneered by Apple, had dethroned the US firm as the world's top smartphone vendor in the third quarter of 2011.

The South Korean electronics giant then went on to replace Nokia as the global leader in overall mobile phone sales in the first quarter of 2012.

But Strategy Analytics said Samsung now faces "intense competition from Apple at the higher-end of the smartphone market, from Huawei in the middle-tiers and from Xiaomi and others at the entry-level."

"Samsung may soon have to consider taking over rivals, such as Blackberry, in order to revitalize growth this year," it added.

Even Apple has been surprised by its growth. Chief executive Tim Cook said during an earnings call this week that iPhone demand "has been staggering, shattering our high expectation."

IDC's Ramon Llamas told AFP that Apple is still seeing strong demand in early 2015 but that "it's going to be difficult to maintain that breakneck pace."

He added that "the fact that they attracted a number of Android users gives them growth prospects for 2015."