Vietnam has added to concerns over global supplies of coffee as the South East Asian country's biggest city remains in lockdown.

The exporting hub of Ho Chi Minh has been kept under tough travel restrictions after a surge in cases of the Delta variant of the coronavirus.

Vietnam is a major producer of robusta, the bitter tasting bean used in instant coffee and some espresso blends.

Wholesale robusta bean prices have risen by about 50% so far this year.

The lockdown of the South-Eastern city of Ho Chi Minh means Vietnam's exporters are struggling to transport goods, including coffee beans, to ports for shipment around the world.

The travel restrictions present yet another problem to exporters already faced with a serious shortage of shipping containers and soaring freight costs.

The city and its ports are a key part of the global shipping network that runs from China to Europe.

The Vietnam Coffee-Cocoa Association and other trade organisations have called on the country's government to ease the restrictions to help avoid further delays to shipments and related costs.

Last week, Vietnam's transport minister responded to the concerns by ordering regional authorities in the south of the country to take action to ease unnecessary burdens on the transport of goods, including coffee.

The issues faced by Vietnamese producers are just the latest problem to hit the coffee industry.

Brazil, the world's biggest producer of the premium arabica coffee beans, has seen its crops impacted by drought and frosts.

The worst frosts in Brazil since 1994 have sent the cost of unroasted coffee beans to the highest level seen in close to seven years.

According to reports, the frost damage was so severe that some coffee farmers may need to replant trees, which could mean that its takes them up to three years to resume production.