Japanese market-leader NTT Docomo announced this morning it had surpassed 10 million LTE connections, underlining its position as the world’s second-largest 4G operator.

Docomo said that subscribers to its Xi (‘crossy’) LTE network surpassed the 10 million milestone yesterday (18 February). It means that about one in six of its mobile subscribers now access the new network.

Xi was one of the world’s first LTE networks to commercially launch back in December 2010. Subscribers to the high speed service had reached 1 million in December 2011 and 5 million by August 2012.

The operator offers 32 LTE-compatible smartphones, six LTE tablets and seven LTE data devices.

It plans to make 112.5Mb/s Xi downloads available in 22 cities by March and more than 50 cities by June. LTE base stations supporting 75 Mb/s will be rolled out to 4,000 locations by March and 10,000 by June. A 150 Mb/s download service is to be introduced by March 2014.

According to Wireless Intelligence data, Docomo is the world’s second-largest operator after Verizon Wireless of the US (21.6 million LTE connections in Q4), just ahead of South Korea’s SK Telecom in third (7.6 million).