UPDATE: AUSTRALIA Post in the grip of a mail delivery crisis, with stocks of diesel drying up in Victoria.

A spokesperson for Australia Post said the company would have difficulty undertaking all of its normal mail movements around the state in the next few days, due to insufficient diesel for its trucks and vans.

Recent storms in Melbourne caused local refineries to shut down production, and reopened facilities are still not at full capacity.

The Australia Post spokesperson said BP, which is running at about 60 per cent of capacity, was still supplying a small amount of diesel to the company's Dandenong and Sunshine depots.

But hardest hit are Australia Post's regional centres at Seymour, Geelong, Ballarat, Bendigo and Morwell, where diesel at service stations is severely depleted.

Meanwhile, grain farmers in the swing of harvest are also getting smaller allocations of diesel.

Victorian Farmers Federation grains president Andrew Weidemann said the shortage of supply was probably being noticed more at service stations but farmers weren't getting their full allocations.

He said he'd received an unconfirmed report a fuel company was moving diesel into Victoria from Sydney to deal with shortages.

"It does have an impact. Farmers can't get their full allocation. But I guess it’s about keeping the wheels rolling (at harvest)," he said.

He said harvest was moving south and depended on the weather.

He'd heard some farmers getting 1500 to 2000 litres and of a farmer receiving diesel contaminated with petrol who was hunting for more diesel.

Mr Weidemann said harvesters with 1000-litre tanks could be emptied in 16 hours.

He said farmers often used several harvesters, chaser bins and trucks, which needed diesel this time of year.

"Lucky in our own situation we filled up earlier in the week."

Mr Weidemann said he heard reports diesel supplies at service stations in Bendigo and Colac were low.

It is believed once Shell repairs its production fault over the weekend it may take a few days for the fuel to filter through the supply chain.