On social media, the Arabic-language hashtag #Israel_on_fire began trending, with most tweets expressing pleasure over the outbreak.
Public Security Minister Gilad Erdan told Channel 10 TV news that eight people had been arrested.
He said arson was suspected in about half of the fires and police had found "flammable materials and liquids poured in certain areas".
"We need to be prepared for a new type of terror," he added.