Trump rips up rulebook on trade and businesses are left reeling

US President Donald Trump is ripping up the rulebook on trade that has been in place for more than 50 years.

His latest round of sweeping tariffs, which came into force shortly after midnight on Wednesday, hits goods from some of America's biggest trading partners including China and the European Union with dramatic hikes in import duties.

The president and his allies say the measures are necessary to restore America's manufacturing base, which they view as essential to national security.

But it remains a potentially seismic action, affecting more than $2tn worth of imports, which will push the overall effective tariff rate in the US to the highest level in more than a century.