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Windstorm knocks out power to 1 million customers in Michigan

(Adds details on outages, quotes from utility president)

March 9 (Reuters) - More than 1 million Michigan electric customers, including homes, schools and hospitals, were without power on Thursday after a windstorm caused the biggest outage in state history, utility companies said.

Wind gusts of more than 60 miles per hour (97 km per hour) on Wednesday toppled trees and downed more than 4,000 power lines across the state, which has a population of about 10 million people, Detroit-based DTE Energy Co said.

"This is a very unusual event ... the most significant weather event that we've had in DTE Energy's 100-year history," DTE Electric President and Chief Operating Officer Trevor Lauer said at a news conference on Thursday.

Strong winds and soft soil - caused by unusually warm winter weather and heavy rainfall - led to uprooted trees and brought down power lines and poles overnight at an unprecedented rate, DTE said earlier in a statement.

Crews from surrounding states were arriving in Michigan to help secure power lines, the company said.

Governor Rick Snyder took to social media to warn residents to avoid downed power lines and to be careful when refueling generators. Many traffic signals were out across the state, and Snyder advised drivers to exercise extreme caution.

More than 800,000 DTE customers were affected by the outages, while more than 300,000 customers of Consumers Energy Co, another Michigan utility, were without power, the companies said.

Lauer of DTE advised residents to check on elderly neighbors and others with health or mobility problems while power is being restored, which he said will likely take several days.

"We understand everybody wants to know when the power will be back on. ... Given the sheer size of this storm, we expect the restoration to take multiple days," he said.

(Reporting by Laila Kearney; Editing by Bernadette Baum and Jonathan Oatis)