(5/29/19) - Residents and businesses were asked to avoid downtown Lapeer for several hours Wednesday after what witnesses described as an explosion dislodged manhole covers.

Police said gasoline entered into sewer lines from an unknown source, causing pressure to build up and explode. Emergency crews were handling the situation as a hazardous materials incident.

Lapeer Police Chief Dave Frisch said it started at Nepessing Street and Saginaw Street and traveled west. Several barricades were set up as firefighters asked people to avoid downtown for safety reasons.

The affected areas included Genesee Street to Oregon Street and Main Street to Nepessing Street.

"Right now, we are still in control mode. We do not know how far the extent is or what the concentration levels of the gasoline that are in the sewers are," said Lapeer Police Chief Dave Frisch.

Because of the closures, Lapeer Community Schools warned parents buses might not be able to get to some students. Police later asked people living from Nepessing Street to Oregon to leave as a precaution.

Residents woke up to a loud boom around 4:30 a.m. and some businesses reported raw sewage seeping from floor drains. No injuries were reported.

The evacuations as of noon were only voluntary, but Frisch said authorities may order mandatory evacuations depending on how the situation develops.

"Well obviously if we have some kind of a spark with the fume concentration, it could be very serious," he said.

Authorities lifted the evacuations at 5 p.m. and let everyone return to their homes or businesses.

Young's Environmental Cleanup was working in the area of Nepessing and Saginaw streets, where the gasoline buildup appeared to be the highest. Crews were still trying to determine the source Wednesday afternoon.

The Michigan Department of Environment, Great Lakes and Energy was assisting city crews and Young's Environmental by testing every manhole in the city for levels of gasoline. The survey was expected to end by 4 p.m.

Crews identified a likely source of contamination, but Frisch could not disclose it Wednesday afternoon. Mitigation efforts were under way to limit the amount of gasoline vapors entering the sewer system.