"The weather was a wet, wintry mix," a campaign official told AFP. A separate indoor event was set to go on as scheduled.

One week before election day, both McCain and rival Democrat Barack Obama were in Pennsylvania, battling for the state which voted for the Democratic candidate four years ago but is seen as key to any path to victory for McCain.

But while McCain cancelled his event owing to the weather, Obama paid tribute to thousands of hardy supporters who turned out for a rally in Chester, Pennsylvania despite the bone-chilling rain and driving winds.

"If we see this kind of dedication on election day, there is no way that we're not going to bring change to America," the Democrat said to huge cheers at the outdoor rally.

"A little bit of rain never hurt anybody," Obama said, "although I've got to say I saw (Pennsylvania Governor) Ed Rendell back stage and his teeth were chattering.

"This is an unbelievable crowd for this kind of weather," he added, gently ribbing some supporters for holding up signs saying "stop global warming."

"This is probably not the weather to hold up those signs. I'm not into global warming either but it's a little chilly today."

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