* Power restoration expected to take up to a week
* Many without air conditioning in predicted triple-digit heat
* States of emergency in Ohio, Virginia, West Virginia
* AT&T National golf tournament closed to spectators
By Ian Simpson
WASHINGTON, June 30 (Reuters) - About 3.4 million people were without power in the eastern United States on Saturday from powerful thunderstorms that stretched from Indiana to New Jersey accompanied by record heat.
States of emergency were declared in Ohio, Virginia and West Virginia because of overnight storms with hurricane-force winds that knocked down trees and power cables along a 500-mile-long stretch. At least eight people were killed.
Forecasters predicted more severe thunderstorms partnered with renewed heat on Saturday.
Restoring power in some areas could stretch into next week and utilities in Ohio and Virginia described damage as "catastrophic."
"It's going to be a while before some folks get power, and with the heat, that's our big concern," said Bob Spieldenner, a spokesman for the Virginia Department of Emergency Management.
More than 1 million Virginia customers were out of power in the worst outage not linked to a hurricane in the state's history, he said.
Six people were killed in Virginia in storm-related incidents, Spieldenner said.
About 800,000 customers in Maryland were without power, and every county in the state had reported outages, a spokesman for the state's emergency agency said.
In West Virginia, Governor Ray Tomblin declared a statewide emergency. A spokesman for the state's emergency management office said about 672,000 people were without power.
The storms knocked out power across two-thirds of Ohio, and Governor John Kasich declared a statewide state of emergency. He said that power could take a week to be restored.
Ohio utilities AEP Ohio and Duke Energy reported a total of about 710,000 customers were out of power.
In Atlantic County, New Jersey, officials declared a state of emergency and asked residents to stay off roads as they cleared debris and repaired power lines. About 100,000 power customers in the area were without power.
Two cousins, ages 2 and 7, were killed overnight by a falling tree in a campsite in New Jersey's Parvin State Park, state officials said.
In the District of Columbia, the Pepco utility said 68,000 customers were effected and power might not be fully restored until the July 4 holiday.
The Pennsylvania Emergency Management Agency said storms had knocked out electricity to 32,500 customers. About 14,000 customers in Indiano had no power.
Area power companies are calling in crews from utilities in neighboring states to help clear damage and restore electricity.
The widespread power outages come as the National Weather Service forecast another day of record-breaking heat and severe thunderstorms across the Ohio Valley and into the northern mid-Atlantic states.
Records for June were broken on Friday in Washington, Atlanta and Louisville, Kentucky. The mercury hit at least 104 F (40 C) in all three cities, according to the National Weather Service.
The high heat prompted the AT&T National golf tournament at the Congressional Country Club in Bethesda, Maryland, to close the competition to spectators and volunteers on Saturday.
The Washington Suburban Sanitary Commission ordered water restrictions in Montgomery and Prince George's counties because the storms had knocked out power to its filtration plants and other facilities.