BOSTON (AP) -- A mammoth snowstorm is battering the New York-to-Boston corridor and has the potential to be a record-breaker.

More than 18.5 inches of snow has fallen in parts of central Connecticut. More than 16 inches of snow are covering Mansfield, Mass., just southwest of Boston.

The National Weather Service says up to 3 feet of snow is expected in Boston, threatening the city's 2003 record of 27.6 inches.

Throughout the Northeast, 500,000 homes and businesses had lost electricity by Friday night as wet snow, freezing rain and howling winds caused havoc. Most are in Rhode Island and Massachusetts.

Thousands of flights have been grounded. New York City's airports are closed. There's about a foot of snow east of the city.

Boston Mayor Thomas Menino says: "This is a storm of major proportions."

Forecasters say the worst is expected early Saturday.