Blizzards have hit cities in the north-eastern US, with government offices staying shut for a third day. In Washington DC and neighbouring Montgomery County ploughing operations were part suspended "because of the hazardous weather conditions".The National Weather Service said heavy snow and winds gusting at up to 60 miles per hour from Virginia to New York could make attempts to travel life-threatening. The blizzards have come as the region is still dealing with days of heavy snow. Schools closed in New York, for only the third time in six years, and the United Nations said it had closed its headquarters in the city. Washington's bus system has ground to a halt and its subway was partly suspended. Thousands of houses have remained without power in the Washington area.