Switzerland's foreign trade activities suffered in April as strict measures to rein in the spreading COVID-19 pandemic hit exports as well as imports of the Alpine country.

Exports fell 11.7% to 16.7 billion Swiss francs (14.04 billion pounds) when adjusted for seasonal factors, their highest monthly decline on record, while imports slid 21.9% to 12.4 billion francs, their lowest level in almost 15 years, the Swiss customs office said in a statement on Tuesday.

Jewellery and watches recorded the biggest declines with 1.6 billion francs wiped off their export value in April, but exports of machines and electronics, precision instruments and metals were also down.

Switzerland imposed lockdown measures from mid-March and has forecast the worst economic downturn in 45 years due to the COVID-19 pandemic.

The seasonally adjusted trade surplus widened to 4.3 billion Swiss francs in April, from 3.1 billion in March, the customs office said. Without adjustments, the surplus stood at a nominal 4.0 billion francs.

Exports to Switzerland's three biggest export markets, North America, Europe and Asia, declined. Exports to Italy and France that were severely hit by the pandemic fell to their lowest monthly levels in around 20 years.

On the import side, jewellery, chemical and pharmaceutical goods and cars took the biggest hit, accounting for 70% of the decline in imports, the office said.

The Swiss watch federation said in a separate statement that the collapse of watch exports was the result of a standstill in production, distribution and sales and reflected "an exceptional situation rather than a trend in demand".

(Reporting by Silke Koltrowitz; editing by Brenna Hughes Neghaiwi)