The new trade tariffs imposed by the United States and the subsequent jostling among countries for exemptions are a sign of "worrying times for Singapore", Emeritus Senior Minister Goh Chok Tong said on Sunday.

In a Facebook post, he shared his thoughts on the US trade tariffs on steel and aluminium imports, and posted a link to a Sunday Times report on how nations have begun vying for exemptions from the levies.

Noting that this is an indication of "a major change in the international trade order", he said: "It is bad for the world, and especially for countries like Singapore which depend on trade and an open economic environment."

US President Donald Trump sparked a global outcry and fears of a trade war when he announced plans for a 25 per cent tariff on US imports of steel and 10 per cent on aluminium to protect the country's producers. He signed the proclamations on the tariffs last week.

But while the tariffs are also being imposed on US allies, they are able to negotiate for exemptions or lower tariffs, Mr Goh said. "So, as German Chancellor Angela Merkel says, 'It is purely business'."

Mr Trump had granted exemptions to Canada and Mexico, before extending a waiver to Australia.

Soon after Mr Trump opened the door, Brazil, Japan, South Korea, Argentina and Europe clamoured for similar special treatment, while Chinese producers called on Beijing to retaliate in kind.

This jostling among countries prompted Mr Goh to note: "The US is like a heavyweight sumo wrestler browbeating wrestlers of lighter weight."

He said that if the US succeeds with its strong-armed bilateral negotiation on tariffs, other big countries may follow suit.

"Beyond trade, the current liberal international system in which countries have thrived is beginning to disintegrate," he added.

"China may step in to fill the void left by an 'America First' policy, but it will carry different values and rules."

Mr Goh, quoting Singapore's founding prime minister, added: "In a world where, as Lee Kuan Yew once said, 'Big fish eats small fish, small fish eats shrimps', these are worrying times for Singapore."

He said that it is why Singapore and 10 other countries have signed the Comprehensive and Progressive Agreement for Trans-Pacific Partnership to keep international trade open and rules-based.

The trade pact, which strengthens trade among countries in the Asia-Pacific region by significantly eliminating tariffs and non-tariff barriers for goods, will make it easier for Singapore companies to do business in the region.