In the message, Trump said the 10% tariff China paid on about US$200 billion worth of goods sent to the US would go up to 25% on Friday, and a further untaxed $325 billion in goods would soon attract the same 25% tariff.
China is now reportedly considering delaying this week's scheduled trade talks.
US and European market indices were pointing to a lower start today and the benchmark S&P/ASX200 was in negative territory in afternoon trade.
Gold was up several dollars an ounce, above US$1,283 an ounce on the spot market earlier. It had traded over $1,300/oz about a month ago.
Australian gold miners were gaining at the time of writing, with Regis Resources (ASX: RRL) up 1.6%, but the broader metals and mining sector was off about 0.9%.
London is closed for a bank holiday today.
Toronto's metals and mining sector had closed up more than 1.1% on Friday as North American markets finished the week higher.
Pretium Resources (TSX: PVG) was one of the bigger risers, gaining 13.66% as it continues to rightsize its Brucejack mine and announced executive chairman and founding shareholder Dr Robert Quartermaine would retire at the end of this year.
And developer Ivanhoe Mines (TSX: IVN) was up 4.4% to a one-year high, as it lengthened the "bonanza" copper zone at Kamoa North in the Democratic Republic of Congo.