Morgan Stanley has raised earnings estimates on General Motors citing "continued strong performance in Chinese operations and GMAC's mortgage business", according to Forbes magazine.

The report said the research firm raised the first-quarter earnings estimate on GM to $US2.05 per share from $1.85, which hikes the year earnings estimate to $6.30 from $6.10.

But Morgan Stanley reportedly said, "We remain concerned about the auto business in North America and Europe," noting that it had cut fiscal 2004 and 2005 sales estimates.

According to Forbes, the firm also said mortgage operations should slow as interest rates rise later this year. Chinese sales are also unpredictable and, while GM's position in China is strong, margin pressure in the region is likely.

Morgan Stanley rates GM at "equal-weight", Forbes said.