The likely new owner of the UK's Vauxhall, part of GM Europe, could be announced later today. The fate of 5,500 workers, at plants including Ellesmere Port in Merseyside and Luton, rests on the decision.

The work to separate GM Europe from its US parent has already begun. Opel, the German division of GM Europe, said that all the company's European assets, including Vauxhall, had been transferred, debt-free, to Opel, which is GM Europe's largest division, employing 25,000 people. The German government is offering billions of euros of state aid to safeguard as many German jobs as possible.

The formal transfer of Vauxhall's assets to Opel will reinforce fears expressed by union leaders and MPs in Britain that Vauxhall workers could lose out in the restructuring.

Earlier, the contest to take control of GM's European operations intensified at the 11th hour after China's Beijing Automotive Industry Corp entered the fray.

BAIC has expressed an interest in acquiring the owner of Opel, according to reports, hours ahead of today's deadline to choose a buyer for the business. However, it is understood that the approach by China's fifth largest carmaker, made one day after the final bidding deadline, has yet to crystallise into a formal offer.

BAIC is competing with Italy's Fiat, private equity firm Ripplewood Holdings and Canadian parts maker Magna, which emerged as the favourite this week following expressions of support from German politicians.

The German government is a key player in the future ownership of GM Europe because it is providing billions of euros in emergency financing to whoever acquires the business, which owns four factories in Germany and employs 50,000 people in Europe. Magna has received the backing of German politicians after pledging to save as many German jobs as possible – a pledge that was later matched by Fiat.

The German economy minister, Karl-Theodor zu Guttenberg, said this week that there was "signalled interest from China" which is believed to focus on importing Opel cars and technology to China, where they would compete with vehicles already being built by GM, one of the country's biggest carmakers despite its problems in the US.

GM has been forced to put its European operations up for sale amid looming bankruptcy proceedings. The group could file for Chapter 11 protection from creditors before the end of the month as a slump in sales overwhelms its lumbering cost base and debt-burdened balance sheet.

Germany's influence over the sale process has stoked doubts in the UK about the future of Vauxhall. Trade union leaders and MPs warned on Tuesday that Vauxhall's 5,000 British workers feared they would lose out to their German counterparts in the deal, after Magna and Fiat made overt promises about jobs in Opel's main European base.

Tony Woodley, the joint general secretary of the Unite union, warned that one or both of GM's two Vauxhall plants in the UK would close if Fiat was selected.

It has also emerged that as recently as the weekend, British ministers did not know whether the three bidders were planning to save or scrap the UK plants at Ellesmere Port and Luton.

Lord Mandelson, the business secretary, has met the three bidders and told them he expected them to commit to the UK. Despite this, the government has not offered the companies any financial backing to keep the plants open and no application has been made by any bidder for loan guarantees under the government's £2.3bn aid package for the motor industry. Any grant is likely to be made only once the German government's plans become clear.