Bidding on General Motors Co.'s Opel European unit is heating up this week, with RHJ International SA (RHJI.BT) expected to offer around $300 million for majority control in the car maker, a person familiar with the situation said Tuesday.

The offer from RHJ International, a Brussels-based holding company, is expected as soon as Wednesday. In addition, GM will likely get a tweaked bid from Magna International Inc. (MGA), the Canadian-Austrian auto parts maker that had previously been the frontrunner, the person familiar said.

GM had anticipated Magna may drop out of the running amid intensifying competition from RHJ and a third bidder, Beijing Automotive Industry Holding Co. Ltd. Instead, Magna, which has remained confident it would emerge as Opel's new owner, appears to be readying a deal for this week, according to this person.

A Magna spokesperson couldn't immediately be reached for comment Tuesday.

GM, which emerged from bankruptcy Friday with a pledge to become a leaner, more profitable car company, is eager to offload its struggling European arm. Magna in May signed a non-exclusive memorandum of understanding to acquire a majority stake as part of a bid backed by Russia's Sberbank Rossia (SBER.RS) and auto maker OAO GAZ Group (GAZA.RS).

But the deal became shaky after RHJ and BAIC joined the fray.

BAIC plans to invest in Opel in China to ramp up production there by 2015, according to a document dated July 2 and reviewed by Dow Jones. BAIC is offering $990 million in equity for a 51% stake in Opel, with GM retaining a 49% stake. RHJ on Monday announced in a statement that talks with GM were at an "advanced stage," but didn't offer further details.

The Magna deal would include $2 billion in bridge financing from the German government. Talks have stalled amid unresolved issues including intellectual property rights and access to growth markets.

The BAIC offer is attractive in that it involved fewer government funds than the Magna arrangement. But GM remains wary of turning the company over to what could become a key competitor in China, on track to become the world's largest auto market this year.

-By Sharon Terlep, Dow Jones Newswires; 248-204-5532; sharon.terlep@dowjones.com