China's Xiaomi Inc has become the world's third-largest smartphone vendor just three years after first hitting the market, trailing only Samsung Electronics Co Ltd and Apple Inc, according to a new industry study.

Strategy Analytics said Xiaomi accounted for 6 percent of all 320 million smartphones shipped during July-September. Samsung made up 25 percent, down from 35 percent a year earlier due to rising competition from several directions.

Apple's share also fell slightly to 12 percent.

"Xiaomi was the star performer," Strategy Analytics Executive Director Neil Mawston said in a statement.

"Samsung continues to face tough competition from Apple at the higher-end of the smartphone market, from Xiaomi and Huawei in the middle-tiers, and from Lenovo and others at the entry-level."

Xiaomi has been the top seller in its home market of China and recently entered India, where it sells phones exclusively through e-commerce site Flipkart.

Vice President Hugo Barra told Reuters in Bangalore last month that the company aimed to sell 100,000 phones a week in India in October when the country celebrates Diwali.