US President Donald Trump has threatened to hit China with an additional 50 per cent tariff and vowed to press ahead with a trade war, reports London's Financial Times.

The threat came after acute tumult on global equity markets, as Wall Street's blue-chip S&P 500 index swung in a huge range. Asian markets regained ground after big falls.

President Trump said he would increase tariffs on China within hours unless Beijing scrapped the retaliatory tariff it announced on US goods.

"If that tariff isn't removed by tomorrow at 12 o'clock, we're putting a 50 per cent tariff on above the tariffs that we put on," he said. "They've become a rich country?.?.?.?I have great respect for China, but they can't do this."