Washington, Jan 15 (Xinhua) Ice storms continued to batter central US states, killing at least 21 people, the National Weather Service (NWS) said Monday.

Since last Friday, waves of freezing rain, sleet and snow have caused at least 12 deaths in Oklahoma, six in Missouri, two in Texas and one in New York, it said.

A state of emergency has been declared and the National Guard called out in Missouri after the storms knocked out power to 200,000 homes.

Churches cancelled Sunday services and businesses closed early or stayed shut.

The NWS said the storm system will head northeast, threatening to bring more than 30 cm of snow to New England.

The extreme weather downed trees, traffic lights and power lines and blocked roads in Missouri and Oklahoma, where some 100,000 homes are without electricity.

Oklahoma Governor Brad Henry has asked the federal government for assistance in handling the consequences of the storm.

In Texas, 415 flights were cancelled Sunday at Dallas-Fort Worth International Airport.

Record-breaking cold weather even hit California, which usually has mild temperatures year-round.

The NWS said it was "a very, very big cold front". It said the storm is gathering moisture from the Gulf of Mexico and cold air from the Arctic, and is expected to hit the east coast Tuesday.