Oct 24 (Reuters) - Wildfires burned across Southern California for a fourth day on Wednesday.

Following are some key numbers:

* 18 active fires from Los Angeles County to the Mexican border

* More than 500,000 people evacuated, largest number in California history, most of them in the San Diego area.

* More than 1,436 homes lost, 25,000 structures threatened statewide

* More than 14,000 people in 38 shelters

* Six people dead, around 40 injured, including at least 18 firefighters

* 426,000 acres (172,400 hectares) or 666 square miles burned

* Seven Southern California counties declared major disaster areas

* $1 billion estimated damage to homes in San Diego County alone

* Hot winds gusting up to 40 to 50 mph (65-80 kph)

* About 10,000 firefighters battling flames

Sources: California Office of Emergency Services; San Diego City Hall, San Diego County.

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