Mr Reid then cut down a second tree which became "hung up" against another tree, before starting on a third.
A few minutes later, the second tree gave way and collapsed upon him.
Mr Thomas said he was making his way toward Mr Reid on his machine when the first tree fell, and when he cut down the second, he jumped off and began running.
Though he could not see Mr Reid, and suspected he was on the other side of the fallen tree, he suspected something bad had happened.
"Straight away I had a gut feeling that I needed to go check on him."
Mr Thomas said that Mr Reid, who had only been felling trees for five days, said his trainee had shown confidence he was able to be aware of all the dangers.
"I wish he had never started that morning and waited for me."
Mr Thomas told the inquest he believed there was nothing he could have done to prevent the death, remarking that everything had been "running smoothly" before the tragedy.
When asked if he agreed that Mr Reid should have been under more direct and close supervision, Mr Thomas disagreed.
He said he had been able to work at a "visual distance" from Mr Reid, from where he could keep an eye on him and communicate visually with him.
But after the first tree fell, Dr Bain questioned why Mr Thomas did not get off the machine then or try to communicate with Mr Reid by yelling or radio.
The inquest continues this afternoon with evidence from Murray Clunie, the director of Great Lake Harvesting, which employed the gang.
Earlier, Dr Bain cited concerning statistics around the industry, noting that the 10 forestry deaths recorded last year were seven times the average of Australia.
Over the past six years, 4,500 forestry workers were recorded as working in New Zealand, compared with 6,800 in Australia and 29,000 in Canada.
Yet the rate of deaths in New Zealand over the period was four times that of both countries, he said.
More than 30 workers were killed between 2007 and 2013, and the rate of ACC claims for work related injuries in the industry was six times the rate for all sectors, he said.
Dr Bain said it was hoped the inquests would prove "the beginning of a path" to prevent forestry deaths.