New Zealanders in Kiwisaver are urged to stay calm and stay the course as stock markets tumble.

The global uncertainty comes off the back of US President Donald Trump's sweeping tariffs on imported goods from the rest of the world.

Simplicity Chief Economist Shamubeel Eaqub says tariffs have caused significant damage to the global economy in the past - and the uncertainty has added to existing economic pressures.

"We really gave it up around the world after the first world war, because we had the depression and we saw the extraordinary damage that it does to our own people and to the global economy. But we also don't know if these policies will actually last the distance - there's so much uncertainty."

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