Chief executive Lei Jun introduced the Mi Note, saying it was shorter, thinner and lighter than the iPhone 6 Plus.
Priced at 2,299 yuan ($371; ?244), the 16 gigabyte model is less than half the price of Apple's handset and Samsung's phablet, the Galaxy Note 4.
Analysts say Xiaomi became the world's third bestselling phone firm in 2014.
The firm - which was only founded in 2010 - announced that the Mi Note was 6.95mm (0.27in) thick and weighed 161g (5.7oz).
That makes it 1.05mm thinner than the iPhone 6 Plus and 11g lighter.The flagship Mi Note Pro has a higher resolution display and a faster processor than the basic model
It also features a 13 megapixel rear camera, made by Sony, and a 4MP front one.
In addition, Xiaomi announced the higher-end MiNote Pro, which will be released at a later date. It has:a higher resolution 2K display (515 pixels per inch) a faster 64 bit Snapdragon processor and 4G chip, which is capable of 450 megabits per second (Mbps) downloads more RAM memory (4GB) 64GB of built-in storage
It will retail for 3,299 yuan ($532; ?350).Price war
Wee Teck Loo, head of consumer electronics research at the Euromonitor consultancy said the flagship devices basically extended what Xiaomi was good at - models that were targeted at Apple and Samsung, the only firms that still outsell it.
"The new models are definitely an upgrade compared to their predecessors - Xiaomi desperately needed to refresh its line-up to keep up with its competitors," he said.
"Xiaomi definitely triumphs its competitors on its pricing."
The Beijing-based firm overtook global market leader Samsung last year to become the top-selling handset brand in the world's largest smartphone market, China.
Just last month, Xiaomi was also dubbed the world's most valuable "technology start-up" after it raised $1.1bn (?708m) in a funding round, giving it a valuation of $45bn.Unlike some rivals, Xiaomi makes a virtue of the fact that other firms make the components it uses, including a camera by Sony and a screen by Sharp
That surpassed the $40bn value of taxi booking app Uber.
The Chinese company reported that its revenue in 2014 more than doubled to 74.3bn yuan (?7.8bn; $11.97bn) in pre-tax sales last year, up 135% from 2013.
It sold over 61 million phones in 2014, up 227% from a year earlier.
Its soaring sales come despite an intellectual property challenge faced in India last year, where sales were temporarily halted after Swedish firm Ericsson filed a patent complaint.
Despite its strong numbers, Xiaomi's phones are only available in select Asian countries including Taiwan, Hong Kong, Singapore, Malaysia, the Philippines, India and Indonesia.
There has been speculation it might soon announce a move into the US, but there was no mention of this at the latest launch.