HARRISBURG, Pa. — Natural gas and fracturing fluid from an out-of-control Pennsylvania well shot 75 feet into the air before crews could tame the flow of explosive gas more than half a day later, officials said Friday.

The well was brought under control just after noon Friday, about 16 hours after it started spewing gas and wastewater, said Elizabeth Ivers, a spokeswoman for Houston-based driller EOG Resources. EOG is also a major natural gas and oil producer in the Barnett Shale of North Texas, where the company had 12 rigs drilling Friday.

Ivers said she could not immediately respond to questions about how the accident happened. Public safety and protection of the environment are of the utmost importance, the company said in a statement.

The well never caught fire, and no injuries were reported, but state officials had worried that the gas might explode before the well could be controlled. State environmental authorities promised an aggressive investigation of the circumstances surrounding the blowout.

“The event at the well site could have been a catastrophic incident that endangered life and property,” John Hanger, secretary of the Department of Environmental Protection, said in a statement. “This was not a minor accident, but a serious incident that will be fully investigated by this agency with the appropriate and necessary actions taken quickly.” If the agency finds that mistakes were made, it will take steps to prevent similar errors, Hanger said. He did not elaborate on any environmental damage.

There are no homes within a mile of the well, and wastewater containing fracturing chemicals and salt was prevented from reaching a waterway, said Dan Spadoni, an agency spokesman.

The well is on the grounds of a hunting club in Clearfield County, about 90 miles northeast of Pittsburgh.EOG was drilling into the Marcellus Shale, a hotly pursued gas formation primarily under Pennsylvania, West Virginia, New York and Ohio that some geologists believe could become the nation’s most productive natural gas field. Many energy companies active in the Barnett are also active in the Marcellus.

The crew had just finished hydraulic fracturing — in which millions of gallons of water, sand and chemicals are pumped underground to shatter tightly compacted shale and release trapped natural gas — and were clearing debris from the well when gas shot out, Spadoni said.

Workers evacuated the site and contacted the Pennsylvania Emergency Management Agency, he said. Environmental Protection wasn’t notified until 1:30 a.m., more than five hours later.

The polluted water flowing out of the well and into the woods was stopped by a trench and a pump installed by a contractor, Spadoni said. Companies that specialize in securing out-of-control wells were called in, he said.

David Rensink, incoming president of the American Association of Petroleum Geologists, said gas well blowouts are very rare but can be very dangerous to control, as a spark can set off an explosion. Securing one can take days, he said.

Typically, valves called a blowout preventer sit atop a well and allow workers to control the pressure inside, he said. A blowout preventer also figured into the massive oil spill off Louisiana. The device was supposed to shut off the flow of oil in the event of a catastrophic failure but did not.

There are more than 1,000 Marcellus Shale wells in Pennsylvania alone, some of them within view of homes, farmhouses and public roads.

On Friday, a worker blocked a dirt road to the site, while trucks hauling water tanks streamed past him. He said he was not allowed to talk about what had happened.