Hurricane Isabel pummelled America's eastern seaboard yesterday, cutting power to hundreds of thousands of people, causing flooding, uprooting trees, threatening tornadoes and paralysing government in Washington as it headed north.

Gusts of more than 100mph reached the Outer Banks of North Carolina by yesterday afternoon, and were expected to increase as the eye of the storm reached inland.

More than a million people were left without power in Virginia and North Carolina as uprooted trees snapped power lines. Isabel came ashore at high tide, threatening flooding in inland areas, particularly to the north where the ground was already saturated.

President George Bush declared parts of North Carolina a major disaster area, a move that will free federal funds to aid in recovery efforts, the White House said.

Most of the inhabitants of the Outer Banks had already evacuated the area, with more than 100,000 moving to makeshift shelters or heading for higher land, while those who remained were under curfew in some areas. In an attempt to scare curiosity seekers from staying, Virginia Beach police suggested that those who remained write their names in permanent marker on their forearms so they could be identified if injured or killed.

At Howard's Pub on the Outer Banks' isolated Ocracoke Island, bartender James Tucker said he and five other employees resolved early yesterday to "hang out and drink beer until the cable runs out".

Mr Bush left Washington and flew to Camp David, his presidential retreat in the Maryland mountains, to beat the storm.

The president, whose meeting with King Abdullah of Jordan was moved to Camp David, said: "We'll have a nice lunch and then we'll batten down the hatches and spend a good evening with our friend."

The secretary of state, Colin Powell, cancelled plans to travel to Sweden for today's memorial service for the murdered foreign minister, Anna Lindh.

The rest of the capital effectively shut down as the mayor, Anthony Williams, put it on a virtual crisis footing and Congress cancelled all hearings.

Commuter railway networks did not run, and subway and bus services were suspended from mid-morning. Schools and city government offices were forced to close. The storm's full strength was scheduled to hit Washington later today.

"It is big. It is ugly. It is a bad storm and it is heading our way," Mr Williams said. "Now is not the time to go and sightsee."

Airlines cancelled more than 1,300 flights into 19 airports in the north-east, south and midwest, the federal aviation administration said.

The intensity of the hurricane has been downgraded in recent days but was still regarded as sufficiently fierce to prompt the governors of North Carolina, Virginia, Delaware, Maryland and West Virginia to declare states of emergency.

Forecasters issued an expanded tornado warning for eastern North Carolina, eastern Virginia as well as southeastern Maryland and predicted tidal flooding of up to 8ft above normal levels as well as "extremely large and dangerous battering waves".