Detroit's annual battle against arson around Halloween could be tougher this year.

Eleven arsons within 90 minutes earlier this month stood as an apparent challenge to the city's annual mobilization to prevent fires during Devils' Night.

City officials say they need to be all the more vigilant because of Detroit's many empty buildings. Along with tens of thousands of long-vacant homes and buildings, more than 40,000 others recently emptied by the foreclosure crisis could present tempting targets.

Thousands of volunteers will patrol during the three days, dubbed Angels' Night, starting October 29.

Last year there were 136 fires over the Halloween period, with 94 believed to be intentionally set, down from a peak of 810 fires in 1984.