More than two million people along the east coast of the United States have been told to evacuate as Hurricane Irene approaches.
High winds are already battering the North Carolina coast, even though the hurricane has been downgraded to a category-one storm.
The mayor of New York has ordered an unprecedented evacuation of a quarter of a million people living in low-lying parts of the city.
Seven states from North Carolina to Connecticut have declared emergencies ahead of Irene's arrival. Fifty-five million people are potentially in its path.
US President Barack Obama has warned Irene could be "a historic hurricane" and has urged people in its projected path to take precautions.
"We all hope for the best, but we have to be prepared for the worst," he said before cutting short his holiday in Martha's Vineyard, an island on the Massachusetts coast, a day early to head back to Washington.
The National Hurricane Center has downgraded Irene from a category two to a category one hurricane but says it is still packing winds of 150 km/h.
The New York subway, which carries some 8.5 million people each day, was to close from midday on Saturday.
Mandatory evacuations have also been ordered in parts of Delaware, Maryland, New Jersey and North Carolina. Transit systems in Philadelphia and New Jersey were also being closed down.
Hundreds of flights have already been cancelled and airlines are predicting widespread disruption.
The storm has already battered the Caribbean, causing flooding that killed at least one person in Puerto Rico and two in Dominican Republic. It knocked out power in the Bahamian capital, Nassau, and blocked roads with trees.
Kiwis' annual picnic cancelled
Because of the storm a New Zealand expat group, the Kiwi Club of New York, has cancelled its annual picnic for the first time in 25 years.
About 200 people turn up every year for the picnic in Westchester County, upstate New York.
The club's president Aaron Snodgrass, says in the 11 years he has lived in the city the subway has never been completely shut down either, but there are fears of flooding.
He says the club wanted people to be at home safe and not travelling through tunnels and subways to get to the picnic.
Mr Snodgrass says many people have been out enjoying a fine evening in the city, buying supplies to last for what's expected to be a very wet and windy weekend.
He himself lives on the 12th floor of a 40-storey building in Jersey City next to the Hudson river. If the wind gets up to more than 110 km/h, he says, his family will be evacuated.
Eerie silence on city streets
The New Zealand consul-general in New York, Paul Gestro, says it's a strange feeling in the city centre, with an eerie silence on quiet streets.
Mr Gestro says he has seen some last-minute panic buying as people prepare for the storm.
He says he has spent the day taking calls from New Zealanders wanting to know what to do if they get in trouble, and setting up contingency plans in case the storm creates a major emergency.
About 1500 New Zealanders live in New York.