ALLENTOWN - A blowout at a natural gas well in rural northern Pennsylvania spilled thousands of gallons of chemical-laced water Wednesday, contaminating a stream and forcing the evacuation of seven families who live nearby as crews struggled to stop the gusher.

Chesapeake Energy Corp. lost control of the well site, near Canton in Bradford County, around 11:45 p.m. Tuesday, officials said. Tainted water continued to flow Wednesday afternoon, though workers had finally prevented any more of it from reaching the stream.

No injuries were reported, and there was no explosion or fire.

"As a precautionary measure, seven families who live near the location have been temporarily relocated until all agencies involved are confident the situation has been contained. There have been no injuries or natural gas emissions to the atmosphere," Chesapeake spokesman Brian Grove said in a statement.

A piece of equipment failed late Tuesday while the well was being hydraulically fractured, or fracked, Chesapeake said. In fracking, millions of gallons of water, along with chemical additives and sand, is injected at high pressure down the well bore to break up the shale and release the gas.

State environmental regulators were taking water samples from the unnamed tributary of Towanda Creek on Wednesday but did not report a fish kill. Towanda Creek is stocked with trout.

Officials advised a neighboring farmer to keep his cows from drinking surface water, said Katy Gresh, a spokeswoman for the state Department of Environmental Protection.

She said reports from the scene indicated that fracking water was gushing from the wellhead, pooling on the pad, then escaping containment.

"Discharge of fluids to the unnamed tributary appears to be stopped," Gresh said.

The blowout came amid a gas-drilling boom in the Marcellus Shale formation below Pennsylvania and neighboring states. Fracking allows affordable access to natural gas that once was too expensive to tap. Critics complain that the chemicals may be contaminating water supplies.