NTT DoCoMo, Japan’s largest largest mobile operator, has announced that its Xi 4G-LTE service has passed 10 million subscribers, doubling its numbers from 5 million customers in August 2012.

The operator, which has a 46 percent domestic market share, claims to support a peak downlink speed of 100 Mbps, but says it is working to increase that to 112.5 Mbps. The burst of speed is slated to come to 22 cities next month, with DoCoMo aiming to have the speedier service live in a total of 50 locations by June.

The Xi (pronounced ‘crossy’) network was launched in December 2010, taking one year to hit the magic 1 million subscriber mark. Now, more than two years later, the service has reached 10 million thanks to a maturing consumer market and the increase in supported devices. The operator’s range of LTE products includes 32 smartphones, six tablets — which includes Windows 8 models — and seven data terminals.

It’s difficult to compare DoCoMo’s progress to the US market. America’s operators don’t break out specific LTE subscriber numbers, instead preferring to focus on the possible reach of their networks and sales of LTE-enabled devices.

According to their most recent financial reports, the Verizon service is available to more than 200 million people, while AT&T covers a total of 135 million. Sprint recently added 57 new locations to its network, and revealed it had sold more than 4 million LTE-enabled phones during its last quarter.

There’s little doubt that Japan, the US and Korea — where SK Telecom has 7.5 million LTE users — are three of the world’s most developed 4G markets, even if confirmed figures are difficult to come by.

Last year, Strategy Analytics estimated that 2012 would see 50 million global LTE subscriptions. That figure was also cited by a report from Parks Associates which crunched the data in July. ABI Research had earlier predicted that worldwide shipments of 4G-compatible smartphones and tablets would reach 61 million during the year.

Headline image via TOSHIFUMI KITAMURA / Getty Images