The government will do all it can to find to find a buyer for one of the country's biggest oil refineries after it fell into administration, and insists there is "no question" of fuel supplies running out.

Coryton refinery in Essex, which supplies 20% of fuel in London and the South East, has halted sales and told its staff it was unsure when supplies would start again.

The refinery was operating as usual on Tuesday but no deliveries of petrol or other products, including bitumen, were leaving the site.

Petrol deliveries to garages and supplies of bitumen for road building and repairs will be affected "pretty soon", unions believe.

The AA said recent disruption at refineries had been short-lived, adding that its main worry was the possible effect on fuel prices.

The shutdown at the former BP-owned refinery - with a capacity of 175,000 barrels of crude oil per day - came as Zurich-based owner Petroplus said talks with its lenders had broken down and it had appointed a receiver to the UK refinery.

Linda McCulloch, national officer at the Unite union, said: "One thousand jobs are at risk but we firmly believe that joint action by the owners and Government can help secure the business."

Energy minister Charles Hendry said the appointment of the administrator was a "very important step forward", adding: "They've been able to hit the ground running because they've been familiar with the issues and therefore need to try and get the plant up and running as soon as possible.

"Major customers like BP and Shell are sourcing the fuel which is needed from other refineries. We've got spare import capacity in the country, so if we needed to bring in more fuel from elsewhere we can do so.

"There's no issue of a shortage arising because of this, we see on a regular basis refineries closing down for maintenance and the country keeps on running as if nothing had happened," he told the Press Association.

"Over the last year a number of refineries here have been sold, there's significant international interest in investing in this sector in the United Kingdom, and therefore there is I believe very good prospects for a new buyer to be found for Coryton."

There are seven other refineries in the UK - at South Killingholme and Lindsey, both in north Lincolnshire; Fawley, near Southampton; Grangemouth, near Falkirk; Stanlow in Cheshire; and Milford Haven and Pembroke, both in Pembrokeshire.

Unite said the energy minister had assured the union that the Government was "exploring all avenues" to find a buyer for the business.

Professional services firm PwC confirmed it was appointed on Monday as administrator to the UK arm of Petroplus, which includes the Coryton refinery, an oil storage site in Teesside and a research and development site in Swansea.

PwC said Petroplus had suffered as a result of "low refining margins and high restructuring costs".

Steven Pearson, joint administrator and PwC partner, said: "Our immediate priority is to continue to operate the Coryton refinery and the Teesside storage business without disruption while the financial position is clarified and restructuring options are explored.

"Over coming days we intend to commence discussions with a number of parties including customers, employees, the creditors and the Government to secure the future of the Coryton and Teesside sites."

The administrator said no redundancies had been made at this stage.

The market has become tougher as the economic downturn in Europe has hit demand for transport fuels and competition has grown from the refineries in Asia.

Petroplus reported a net loss of US$413m (£265m) in the first nine months of last year, while in December its banks withdrew a US$1.05 billion (£675m) portion of its US$2.01 billion (£1.29 billion) credit facility.

The other main supplier for the South East and London is the Exxon Mobil refinery in Fawley, near Southampton.

BP, a major customer of the Coryton refinery, said it had no immediate supply issues but it was "watching the situation very closely".