Executives of MG Rover's engine manufacturer have bid for the car maker's remaining assets as potential buyers were given until tomorrow to submit offers.

If the bid from senior managers at Powertrain Ltd succeeds, production of MG sports cars could resume at the Longbridge site.

However there are no plans for mass production of Rover vehicles such as the Rover 45 or 75.

The would-be buyers from Powertrain, owned by MG Rover's parent company Phoenix Venture Holdings, could find themselves in competition with Shanghai Automotive Industrial Corporation (SAIC), China's state-owned automotive manufacturer.

SAIC was hailed as MG Rover's potential saviour before the Birmingham company went into administration but is now looking at buying parts of the Longbridge operation, including the Powertrain engine factory.

The Powertrain managers involved in the bid are not members of the "Phoenix four", the Rover directors whose conduct has been criticised by workers and politicians since the manufacturer went into administration last month. Sources outside Powertrain who have seen details of the proposals said vehicle production would be limited at first.

A source said: "Eventually, around 3,000 people might one day be employed. That is if things go well."

No details have been released, as those involved have been required to sign non-disclosure agreements.

Meanwhile MG Rover's administrators have given potential buyers until tomorrow to make their intentions clear.

PricewaterhouseCoopers has asked interested parties to finalise their expressions of interest in parts of the Longbridge carmaker before it moves to the next stage of administration.

About ten interested groups have been around the factory site to inspect the facilities and 70 information packs have been sent out so far. No firm offers to buy the whole business have been received so far, but SAIC has written to expressing preliminary interest in some of the assets.

PwC said it had been in discussions with a number of interested parties would not comment on any negotiations or potential purchasers.

SAIC, which pulled out of its joint venture with MG Rover last month, has expressed an interest in tooling for the Rover 25 and 75, as well as a parts of the assembly line and equipment for the two models.

It also expressed an interest in parts of the Powertrain engine factory and the research and development facilities.

The costs of running the site, where 500 people are still employed, could force PwC to start realising assets.

It is estimated to be costing £1.5 million a week to carry on running Longbridge while PwC has sought to sell the operations as ongoing businesses. It could now be forced to sell off plant and machinery piecemeal.

Rob Hunt, a partner at PwC and joint administrator, said: "We have asked people to finalise their expressions of interest. Then we are going to have to have a serious sit down and consider this next week.

"If nothing is forthcoming then we will have to move to exit sooner rather than later. We will look to start selling parts of the business bit by bit.

"It is losing money and we cannot carry on like that."

Mr Hunt said there had been expressions of interest in all parts of the business, and had been whittled down to companies which had a serious interest and the capability to take on parts of MG Rover.

At present 400 people are still working at MG Rover and 100 at Powertrain, finishing off models, engines and tidying up the factory.

Others are involved in the finance operation and servicing the retail network. Mr Hunt said these jobs would continue until the end of this month.

He added: "We have no intention at the moment of bringing that number down."