Several thousand people gathered for a demonstration in Sweden on Tuesday to call for iconic Swedish carmaker Saab to be rescued from its owner GM's plan to shut it down.

"There were at least 3,500 people at the demonstration, including Saab employees, employees from neighbouring companies and town residents," Paul Åkerlund, the head of the Saab branch of the IF Metall union, told AFP.

The demonstrators chanted "Save Saab! Save Saab!" during the half-hour protest outside Saab's headquarters in the southwestern Swedish town of Trollhättan, he said.

According to Swedish news agency TT, other signs and banners read "Mr Obama -- Please Save Saab" and "GM -- General Mistake."

General Motors announced on December 18 that it would wind down the brand which has barely turned a profit during two decades under GM ownership, but several groups have since made last-ditch bids for it.

They include Dutch sportscar maker Spyker, a group comprised of Formula One boss Bernie Ecclestone and Luxembourg investment firm Genii Capital, and a Swedish group fronted by the former chief executive of German truck manufacturer MAN and a former politician.

GM has said it would still consider offers for Saab even though it has begun the wind-down operations.

But on Monday GM chief executive Ed Whitacre told Swedish news agency TT that none of the eleventh-hour bids were strong enough financially.

He said: "Give us 450 million dollars and the situation would be different."

The financial details of the bids have not been disclosed.

Saab unions on Tuesday sent an open letter to Whitacre urging him to sell the brand instead of shutting it down.

"Show us that GM is a responsible multinational company," read the letter, a copy of which was obtained by AFP.

"Show us respect as employees within GM! Show us that you represent moral and integrity! Show us that you keep promises! SAVE SAAB -- SELL SAAB!" it said.

Saab, which employs 3,400 people in Sweden, is one of four storied brands being shed by GM as part of a massive restructuring effort that began in 2005 and accelerated last year when the largest US automaker went bankrupt.

Analysts have warned that some 8,000 jobs could be lost with Saab's closure.