DETROIT -- Violent thunderstorms rattled Michigan's northern Lower Peninsula as utility crews raced to restore electrical service to 20,000 remaining metro-Detroiters without power ahead of another round of rough weather.

Detroit Energy spokesman said Friday's storms have left another 37,000 customers without power in southeast Michigan.

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The most severe weather hit Lake, Mason, Missaukee and Wexford counties in northwest Lower Michigan. The National Weather Service issued tornado warnings for those counties, but canceled them by 1 a.m. Friday.

Sheriff's officials in Mason and Lake counties said they had received no immediate reports of injuries or property damage.

"Lots of lightning, lots of thunder," Sgt. Bethany Carrier said Thursday night from the Mason County sheriff's office in Ludington. "There's been 60 mile-an-hour winds."

Flash flood warnings were in effect overnight for Lake, Manistee, Mason, Missaukee and Wexford counties, the weather service said. More than 4 inches of rain fell between 9 p.m. and 11:45 p.m. Thursday near Scottville in Mason County, forecasters said.

Authorities on Friday morning advised drivers in the county to stay off roads unless it was an emergency. The sheriff's office said in a statement that numerous roads and bridges had become unstable or impassable because of excessive rain.

The county closed or barricaded more than a dozen roadways, including parts of U.S. 31, U.S. 10 and M-116 south of Ludington State Park.

Utility crews from as far as Missouri and West Virginia were helping restore service to 57,000 southern Lower Michigan homes and businesses still without power from a wave of severe storms that hit a week ago.

The thunderstorms pushed across the state June 6 through Tuesday, knocking out power to at least 730,000 utility customers and claiming eight lives.

IMAGE GALLERY Severe Storms

Still lacking electrical service were 57,000 of 360,000 affected customers at DTE Energy Co., 250 of 350,000 at CMS Energy Corp. and 500 of about 20,000 at Lansing Board of Water and Light.

DTE crews are still working to restore power to 35,000 Detroit residents that have been without power all week. In addition, they are trying to get to an additional 25,000 customer's who are in the dark after Friday's storm.

The hardest-hit area was Oakland County, with 33,000 reported power outages remaining. About 9,000 Macomb County residents are still in the dark and 1,500 Wayne County residents are without power. Livingston County is now added to the list of outages with 8,500 customers offline. The rest of the outages are scattered.

DTE said they are hoping to have everyone online by Sunday-- at the latest.

DTE MAP OF POWER OUTAGES

DTE spokesman John Austerberry says 650 company linemen and about 450 from other utilities were working to restore power.

Austerberry said service to some customers might not be restored until Sunday, and there could be further delays if thunderstorms forecast for Friday are severe. The weather service said southeast Michigan could be threatened with damaging wind gusts and torrential rainfall Friday.

DTE suggests homeowners to report their outages at www.dteenergy.com or www.mydteenergy.com because they were having problems with their phone lines Monday.