Rescuers are desperately searching for a grandmother they believe fell into a deep sinkhole -- holding out hope of finding her despite the difficult rescue conditions.

Elizabeth Pollard, who was last seen Monday evening, has not yet been found amid the complicated search effort in Unity Township, Pennsylvania, police said midday Wednesday.

The sinkhole is believed to be tied to an abandoned coal mine and formed while Pollard was walking in the area, officials said. Search crews were able to make entry into the mine area, though the integrity of the mine has been compromised by the water they are using to break up the ground, Pennsylvania State Police Trooper Steve Limani said during a briefing Wednesday.

Search crews will no longer be sent into the mine due to the danger of collapse, with the search effort shifting to cameras, according to Pleasant Unity Fire Chief John Bacha.

The search will continue as long as needed pending any safety concerns, though the digging process may be slower now, Limani said.

"Hopefully she's in an air pocket," Limani said during a briefing Tuesday evening, noting that there have been incidents in the region where people have survived similar situations in underground mines. "This is a rescue to me until something says that it's not."

The conditions are tough, with clay-like soil making it difficult to dig, but rescuers remain determined.

"We're doing everything we can, and no one is giving up," said Limani.

He added, "It's heartbreaking for her family and everyone here. But we're not stopping. We're all hoping for a miracle."

Pollard was reported missing by a family member shortly before 1 a.m. Tuesday, Limani said at an earlier press conference Tuesday.

Pollard was last seen around 5 p.m. Monday, Limani said. The family member said Pollard had gone out to look for her cat Monday afternoon but has not been heard from since, he said.

Pollard's vehicle was located shortly before 3 a.m. Tuesday with her 5-year-old granddaughter inside, though Pollard was nowhere to be seen, police said.

"At that point in time we realized this could be a very bad situation," Limani said.

While searching for Pollard in the area, troopers found an apparent sinkhole with an opening about the "size of a manhole" 15 to 20 feet away from the vehicle, Limani said.

Emergency responders were called to the scene in what is currently being considered a rescue mission, authorities said. Local firefighters, a technical rescue team and the state's Bureau of Mine Safety are among those working alongside an excavation team to remove dirt to access the sinkhole, Limani said.

The current evidence points toward Pollard being in the sinkhole, Limani said.

"We don't feel a reason that we should be looking elsewhere," he said.

The sinkhole appears to have been created during the time that Pollard was walking around, Limani said, noting there is no evidence the hole was there before she started looking for her cat.

The area where the sinkhole formed has a "very thin layer of earth" and appears to have been deteriorating "for a long time," Limani said.

"It appears to be mostly just grass interwoven where she had stepped," he said. "There wasn't much earth at all to hold up that space."

A camera inserted into the opening of the sinkhole showed a "big void, and it was all different depths," Marguerite Fire Chief Scot Graham told reporters during the earlier press briefing.

A camera did not pick up any sounds, though authorities did see a "modern-type" shoe in the sinkhole, Bacha said. The shoe has not been recovered amid the excavation, he said Wednesday.

"The process is long and it is tedious," Graham said of the search effort.

The mine last operated in 1952, according to the state's Department of Environmental Protection. The depth to the coal seam in this area is approximately 20 feet, a department spokesperson said.

Once the scene is clear, the department will investigate the site "to determine if this issue is the result of historic mine subsidence," the spokesperson said.

Pollard's granddaughter is safe, despite the cold temperatures overnight, and is currently with her parents, Limani said.

The family is asking for privacy at this time and is hoping for "good news," he said.

"We need to get a little bit lucky," Limani said. "We're going to do everything we can."

ABC News' Alexandra Faul and Jason Volack contributed to this report.