DAISETTA, Texas – A massive sinkhole that has swallowed oilfield equipment, telephone poles and vehicles grew overnight but isn't much closer to the main road running through this small town, officials said Thursday.

Cpl. Hugh Bishop with the Liberty County Sheriff's Office said the sinkhole is now about 600 yards in diameter and anywhere from 150 to 250 feet deep.

There were no reports of injuries or homes being damaged in Daisetta, a town of about 1,000 residents located about 60 miles northeast of Houston. The sinkhole first began growing Wednesday, and officials are still trying to figure out what prompted it.

"It is a bit bigger," Bishop said Thursday morning. "But the main part we were worried about, encroachment on the roadway, that part hasn't materialized. It has grown in other directions."

Officials have been worried the sinkhole could endanger Farm-to-Market Road 770, which has been closed to traffic. Schools and businesses remain open.

There are about 100 homes in the immediate area, but the nearest to the sinkhole is about a quarter of a mile to half a mile away. Bishop said.

"Once it stops moving or stops growing, we can get in there and take a better look," he said.

Investigators with the Texas Railroad Commission were checking pipelines and trying to determine if any regulations have been violated, agency spokeswoman Ramona Nye said. Officials with Texas Natural Resources and Conservation were monitoring air and water quality. So far, no pollutants have been detected.

"Right now we're not concerned about any kind of explosion or any kind of hazard," said Tom Branch, coordinator of the Liberty County Office of Emergency Management.

Sunoco, which manufactures petroleum and petrochemical products, secured two 6-inch crude oil pipelines near the sinkhole that had started to leak Wednesday, said Lester Edwards, hazardous materials coordinator for Liberty County.

Television news footage showed a tractor, oilfield equipment and telephone poles falling into the sinkhole as it grew near Daisetta.

While the cause of the hole isn't known, once-booming oil town's history might be to blame.

The ground might have caved in because of the collapse of an old salt dome where oil brine and natural gas are stored underground, officials said. Daisetta sits on a salt dome, one of the most common types of traps for oil.

Sinkholes are rare and often take up to two weeks to stabilize, said Geoffrey Paine, a geologist and geophysicist with the University of Texas.