* Southwest Ontario hit by violent winds and heavy snow
* Police rescued nearly 240 people stranded by storm
* Storms disrupts some auto production (Updates police statement on number of rescues)
TORONTO, Dec 14 (Reuters) - Canadian military aircraft helped with the rescue on Tuesday of motorists stranded by an unusually fierce winter snow storm that reduced visibility to near zero and closed a key transport link in southwestern Ontario.
Police rescued nearly 240 people who were stranded in cars and trucks amid deep snow drifts on Highway 402 near Sarnia, Ontario, some overnight from Monday. They were now checking for vehicles that might have been trapped by the snow on surrounding roads.
"We're making great progress," said Ontario Provincial Police Sgt. David Rektor.
A local state of emergency was declared in the area about 70 miles (112 km) northeast of Detroit, Michigan.
"We're talking violent winds and heavy snow ... Some of these cars are stuck in drifts that are four or five feet (1.2-1.5 metres) deep," Rektor said.
Police had initially feared that more than 300 people might have been stranded by the storm, which some drivers told local media had caught them by surprise.
A military airplane and at least two helicopters equipped with rescue equipment were being used to assist ground crews as they tried to reach stranded motorists, Defence Minister Peter MacKay told reporters in Ottawa.
Dangerous weather conditions with drifting snow and a wind-chill factor that makes temperature feel like -20 Celsius (-4 Fahrenheit) were expected to last into Wednesday in some areas near Sarnia, according to Environment Canada forecasters.
No injuries or deaths were reported, but the storm closed a major transportation link between Canada and the United States.
General Motors <GM.N> idled its Oshawa, Ontario, assembly plant as the storm cut its supply of parts. A second GM plant, in Ingersoll, Ontario, was working on partial shifts.
Ford Motor Co <F.N> said it expects the storm will disrupt production at its Canadian assembly plants in Ontario, although Chrysler said it did not expect to have problems.
Canadian National Railway <CNR.TO> said its rail line through Sarnia remained open, although the weather was slowing operations. (Writing by Allan Dowd; editing by Rob Wilson)
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