This screenshot taken on Sept 18, 2020 shows the website of JD Health.

JD Health International Inc jumped in Hong Kong’s gray market trading, a sign that the city’s biggest IPO of the year is off to a good start.

The unit of Chinese mainland e-commerce company JD.com Inc advanced as much as 28 percent to HK$90.55 on Monday on an over-the-counter retail platform operated by Phillip Securities Group. The shares saw similar gains on platforms operated by Bright Smart Securities International (HK) Ltd and Futu Securities International (Hong Kong) Ltd.

The unit of Chinese mainland e-commerce company JD.com Inc advanced as much as 28 percent to HK$90.55 on Monday on an over-the-counter retail platform operated by Phillip Securities Group

JD Health raised HK$27 billion (US$3.5 billion) after pricing its sale of 381.9 million shares at HK$70.58 each, which was the top end of a marketed range, according to terms for the deal obtained by Bloomberg. 

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The offering is the largest of this year’s first-time share sales in the Hong Kong Special Administrative Region -- only a second listing by JD Health’s parent company in June was bigger. The stock starts official trading Tuesday.

Hong Kong has seen a flood of new and largely successful listings this year by companies such as JD.com, NetEase Inc and Nongfu Spring Co.

JD Health said the retail portion of its offering was 422 times oversubscribed, prompting it to boost the number of shares set aside for individual investors in the city to 42 million from 19.1 million under a claw-back mechanism. The number of shares allocated to institutional investors was cut to 339.9 million.

JD Health is the largest online health-care platform and online pharmacy by revenue in the mainland, its prospectus says. The company recorded revenues of 8.8 billion yuan (US$1.3 billion) in the first half of 2020, up from 5 billion yuan in the same period a year earlier.

ALSO READ: JD.com to spin off health unit, list in Hong Kong

JD Health brought in six cornerstone investors for its IPO who agreed to subscribe for as much as US$1.35 billion of stock, including Singapore sovereign wealth fund GIC Pte, Hillhouse Capital and BlackRock Inc Bank of America Corp, Haitong International Securities Group Ltd and UBS Group AG are joint sponsors.

In a so-called gray market, investors can bid for new shares before they officially start trading on an exchange. The early stock moves are often seen as an early indicator of investor demand for the IPO.

READ MORE: JD Health 'plans US$1 billion HK IPO filing this month'