NEW YORK (Reuters) - Manhole covers are being stolen from the streets of New York City, leaving dangerous holes in the roads and sidewalks, authorities said on Thursday.

More than 30 manhole covers have been stolen in the city's Brooklyn, Queens and Bronx boroughs since early March, presumably by thieves selling them for scrap metal, said a spokesman for the Con Edison utility company.

"Stealing manhole covers is dangerous," said Milovan Blair, Con Edison's vice president for Brooklyn-Queens Electric Operations. "Anyone who steals these covers creates a serious hazard for pedestrians and motorists."

Witnesses have reported seeing thieves wearing utility-style clothing but without official insignia prying open covers with a car jack, loading them onto pickup trucks and driving away, Con Edison said in a statement.

Manhole covers are stolen on occasion but the recent thefts are a marked increase, said Con Edison spokesman Michael Clendenin.

The covers are made of cast iron or composite materials and can weigh as much as 300 pounds (136 kg), he said. The high price of metals make them attractive to sell as scrap.

(Editing By Ellen Wulfhorst, Greg McCune and Eric Beech)