Hong Kong’s benchmark stock index fell by the most in more than a year, tracking slumps in equity markets across the Asia-Pacific region, as a tit-for-tat tariff war between China and the US sends shock waves through the global economy.

The Hang Seng Index plummeted 9.1 per cent to 20,778.10 as of 10.50am local time. It plunged by as much as 10.2 per cent in intraday trading to 20,508.85, the biggest one-day percentage plunge in more than a week. Across Asia-Pacific, benchmark gauges declined to their lowest in 52 weeks in 11 of the region’s 14 equity markets.

All but two of the 83 Hang Seng Index members dropped, with exporters including PC maker Lenovo Group and optical manufacturer Sunny Optical Technology bearing the brunt of the sell-off.

Stock gauges also plunged on the mainland. The CSI 300 Index, which tracks the 300 largest stocks listed in Shanghai and Shenzhen, fell by as much as 7.6 per cent. The Shanghai Composite Index fell 7.4 per cent while the Shenzhen Composite Index dropped by as much as 9.8 per cent.

Monday’s reaction was the first since US President Donald Trump kicked off his worldwide tariff war against America’s trading partners. The US slapped a 34 per cent tariff on Chinese imports – including those from Hong Kong – on top of levies that were already in place since Trump’s first trade war in 2018.

Markets on the mainland and in Hong Kong were closed Friday to mark the Ching Ming Festival public holiday.