Mainland and Hong Kong shares fell at the open on Wednesday as the US trade war escalated, following Washington's decision to impose 104 percent tariffs on Chinese goods, starting around noon, Hong Kong time.

Hong Kong's benchmark Hang Seng Index sank 3.14 percent, or 632 points, to 19,494, while the Shanghai Composite Index shed 1.13 percent, or 35 points, to 3,110.

Chinese state holding companies continued to support the stock market by increasing share investment, while a slew of listed firms announced share buybacks.

Elsewhere in the region, Japan’s Nikkei 225 index initially lost nearly four percent on opening, and markets in South Korea, New Zealand and Australia also declined.

South Korea's currency meanwhile fell to its lowest level against the US dollar since 2009, while oil prices slumped three percent in early Asian trade. (Agencies)