Luckin Coffee, Starbucks' biggest rival in China, is looking to raise more than half a billion dollars when it goes public in the United States, according to a filing the company issued with the Securities and Exchange Commission Monday.

The company announced plans for a US IPO last month.

China is Starbucks' (SBUX) second-biggest market, after the United States, with around 3,000 stores across the country. It plans to more than double that number by the end of 2022.

But Luckin is catching up quickly — Luckin locations may soon outnumber Starbucks stores in China.

Luckin, which is about 18 months old, has opened more than 2,300 stores across China and plans to open another 2,500 by the end of this year. Most Luckin locations are "pick-up stores" with limited seating that are designed to let customers pick up their orders and leave quickly.

The chain has previously raised hundreds of millions dollars from big international investors including Blackrock (BKCC). Following the company's April fundraising round, it was valued at about $2.9 billion.

— CNN's Daniel Shane contributed to this report.