Zai Lab (HKG:9688) proposed an underwritten follow-on public offering of $200 million of American depositary shares in the US market, according to a Thursday filing with the Hong Kong bourse.

Each ADS represents 10 ordinary shares of the company, carrying a par value of $0.000006 per share. All ADSs are offered exclusively by Zai Lab, which has also granted underwriters a 30-day option to purchase an additional 15% of the ADSs at the offering price, minus underwriting discounts and commissions.

Zai Lab said the net proceeds from this offering will be used toward general corporate purposes.

The company's shares were down by almost 2% in early morning trade.