Seconds later, the small plane disappeared out of sight and then they heard it nose-dive into the ground, killing all four people on board.
"It was doing these spirals but really high up in the air, like at first, we thought it was controlled," said Nicholls, who was out walking her dog.
"But then as we watched, we realized that it didn't look like controlled movements. It looked like it had lost control and it was going down."
Investigators are now trying to piece together what caused the light-coloured Cessna 172 to crash into a cornfield near Moorefield, Ont.
Ontario Provincial Police say three men and one woman were pronounced dead at the scene following the accident, which occurred around 8:30 p.m. Friday.
One of the victims was a 19-year-old woman. The three others were in their 20s, according to police. All were from the Greater Toronto Area.
Nicholls said before the crash, she saw the plane's engine sputtering but as it got closer to the ground, it looked like the pilot had been able to regain some control.
"The pilot got the engine going again," she said. "It was nice and strong, full power, but only for a second or two. Then it just went dead."
She and her husband then raced back to their nearby home to grab a first aid kit and sleeping bag, in hopes of finding any survivors. But when they returned in their pick-up truck, they couldn't locate the crash site.
They then went to a neighbour's house to call 911.
Nicholls said she's distraught over how scared the passengers must have been.
"There was definitely time in their descent for them to be terrified, and it just kind of doesn't sit good with me," said Nicholls, her voice quivering.
Curtis Bults was getting ready to leave for a baseball game when the Nicholls' showed up.
Moments earlier, he had heard strange noises behind his house.
"It sounded like a whiny noise, like a go-kart, like a small plane going 'Eee Eeee Eeeee!,' said the 21-year-old.
"And (then) a couple second delay, and I heard a thud. I heard kind of a shake in the ground."
Bults said his two dogs were "absolutely freaking" from the commotion, which could be heard clearly even though all the house's windows were closed.
He then drove his ATV through the adjacent cornfields to investigate. After about 10 minutes, he returned home after finding nothing.
"I heard it but there was no smoke or anything," said Bultz. "There was no smoke at all. That's what you think, (that) there'd be something but there was nothing."
Bultz said he, his neighbours and emergency crews did a grid search on foot, tractors and four-by-fours.
It wasn't until two hours later that they were able to locate the plane wreckage.
Once it was found, his father used a tractor to carve out a path for the emergency crews to get to the scene, he said.
"It was the middle of nowhere," said Bultz. "It was in the middle of a 50-acre cornfield."
OPP Const. Keith Robb said an emergency transponder signal had been activated when the plane went off the radar around 8:20 p.m.
It's unclear how long the plane had been in flight before it crashed.
At this point, the investigation remains in its preliminary stages but police do not believe weather was a factor.
"It was a clear, sunny night," he said.
Two investigators from the Transportation Safety Board remain at the scene, and are trying to determine whether mechanical failure is at fault. The plane was expected to be removed from the field later Saturday.
Bob Connors, the general manager of the Waterloo-Wellington Flight Centre, said the plane was one of his and it was a rental.
He said the flight school, which operates out of the Waterloo Region International Airport, had not had a crash like this in a "long, long, long time."
Connors would not comment on the pilot's flying experience.
The victims' bodies have been transported to a hospital in Hamilton for autopsies and police were in the process of contacting their families.
By Linda Nguyen in Toronto