African swine fever has been found in two dead wild boar in Belgium and has led to fears that Denmark’s huge pig industry could be threatened.

If the disease spreads, it could jeopardise almost $1.7bn (£1.3bn) in pork-product exports from Denmark.

But some opponents have questioned how effective the $12m (£9m) fence will be.

African swine fever is harmless to humans, but can be carried by both wild and domestic pigs. It is usually fatal within days, and there is no cure and no vaccine.

And Denmark produces about 28 million pigs a year. The industry is worth 30bn Danish kroner ($4.6bn, £3.5bn).

If there were an outbreak of African swine fever, “exports to non-EU countries would have to shut down”, the government said.

The Minister for Environment and Food, Jakob Ellemann-Jensen, said the government was determined “to do everything we can to prevent African swine fever reaching Denmark. And now we can finally get started on erecting our wild boar fence”.

When completed later this year, the border fence will:

• Be 1.5m (5ft) tall, and at least 50cm (1.6ft) deep to stop boar burrowing under
• Have about 20 gaps at border crossing points and waterways
• Have at least one gate every kilometre and steps elsewhere so humans can climb over it
• Have 20cm (8 in) square openings every 100m (300ft) for small animals to move through