iPhone 6 sales are continuing to smash expectations

The iPhone 6 is continuing to sell extremely well.

Apple's latest smartphone has already gifted the company the most profitable quarter of any company ever. Now, UBS is estimating the Q2 2015 sales will be even higher than anyone was expecting.

In a new research note, UBS says it believes Apple will see demand of around 51.1 million units, compared to consensus Street estimates of 45 million.

The financial services company points to a "continued surge" in China as partly behind this success - Apple recently dethroned Xiaomi as the number one smartphone company in the country.

The UBS figure comes from its "Evidence Lab" wing, which has previously been accurate in its predictions compared to the street.

Here's a graph showing UBS Evidence Lab's historical numbers compared to street estimates and actual iPhone sales:

The UBS estimate also bears out a previous prediction from Piper Jaffray analyst Gene Munster. Munster wrote last month in a research note that the iPhone 6 is "fundamentally different" from previous product cycles, and even after its record-breaking sales and profits, people may be underestimating just how well it will sell. He thinks that in calendar year 2016, we may see potential iPhone sales in excess of 250 million.

The iPhone is continuing to see strong growth in European countries, according to data from Kantar Worldpanel, as Apple focuses on persuading "switchers" to dump Android in favour of iOS.

And in China, Samsung - Apple's chief high-end Android competitor - has all but imploded, its market share plummeting by more than 50% in just a year.