Houthi forces fired mortar rounds at an oil refinery in the southern Yemeni city of Aden on Monday, starting a huge fire, witnesses and local officials said.

The mortar barrage hit three full storage tanks, in an incident sure to add to the fuel crisis in the southern port. After months of conflict, most of Yemen's oil and gas industry has ground to a halt.

The attack on the refinery in the Buraiqah area sent black smoke and flames swirling high into the night sky.

"We are trying to put out the fire. The shelling targeted the tanks where we were storing diesel and fuel for local consumption in Aden. The damage is going to be very big," one official at the facility told Reuters on condition of anonymity.

The Houthis, who took over the capital Sanaa last September, have been battling local fighters in the south for three months and had attacked the refinery before.