As many as 50,000 jobs in California are at stake if Toyota decides to close its NUMMI plant in Fremont after GM earlier announced plans to exit the joint venture, a pressure group claimed on Monday.

A Japanese newspaper report last week said NUMMI production would end next March though a Toyota spokesman insisted then that no decision had yet been made.

'Friends of NUMMI' said in a nationally distributed statement there currently are 4,600 jobs at immediate risk while the closure could lead to the demise of up to 50,000 jobs throughout the state of California among suppliers and local businesses "that have worked dynamically to support the automotive plant for the past 25 years".

Opened in 1984 to make Prizm sedans for the now defunct Geo brand, alongside the similar Toyota Corolla, NUMMI was a pioneering joint venture between General Motors and the Japanese automaker and helped change the US automobile industry by introducing the Toyota Production System and a teamwork-based working environment to the United States.

The plant now builds Corolla sedans for Toyota and the Vibe, a model based on Toyota's Canadian-made Matrix, for GM's Pontiac division which is to be axed by the recently reorganised automaker. The Japanese newspaper report last week said Toyota would move NUMMI's Corolla output to its plant in Ontario, Canada, and Tacoma truck output to its (under-utilised) new truck plant near San Antonio, Texas.

Friends of NUMMI said the plant has 1,000 suppliers based in California employing 50,000 people.

The organisation representing families, workers, suppliers and local businesses that will be affected by the closure is urging local, state and federal officials to persuade Toyota and the newly reorganised General Motors "to consider the total loss in jobs, the impact on suppliers, local businesses and families that will be devastated by the plant's closure, as well as the impact on the already distressed economy", the statement said.

"In addition, the closure will lead to substantial losses in local and state revenues and employment taxes; it will increase property foreclosures which will lead to a drop in attendance in local schools due to affected families requiring relocation, and significantly increase the unemployment claims - significant concerns that California's struggling economy can't afford."