UK's Road Haulage Association (RHA) has warned that supply chain between Northern Ireland and the UK could stall amid the new rules on Brexit.

A little more than a week after the UK left the European Union, some sectors are already experiencing problems, the RHA said in a letter sent to Cabinet Minister Michael Gove.

The British-run Northern Ireland region falls into both camps - part of the UK customs territory, but still focused on the EU single market for goods, even though the UK is no longer part of the EU single market and customs union.

The shelves of supermarkets were empty last week, despite efforts to import fresh goods from the UK. Manufacturers said that trucks bound for Northern Ireland are unable to cross the Irish Sea due to difficulties with customs declarations.

To add to that, the RHA said supply lines have been restricted due to legislative changes, and factories have already reported serious supply chain problems, including non-compliance with retail contracts.

Earlier, the trade authority already warned the government that introducing some of the most complex customs processes in the world, especially amid the COVID-19 pandemic, will leave shelves empty and lead to shortages of goods and materials.

The executive director of RHA, Richard Burnett, also warned that the current lockdowns will leave Northern Ireland's tourism sector and non-essential retailers closed for another month, adding that this is "just a disguise for the crisis in the food and tourism supply chain."

On Friday, Gove said that difficulties in moving goods between Northern Ireland and the rest of the United Kingdom will get worse, before they adjust and recover.