He said he gave the teenager a medical examination after she complained of sore ribs and a bruised head, but claimed "it was weird, the situation was unusual".
King said he began to suspect the other people in the home had physically assaulted the teenager.
"I thought to remove her from the home and into the back of the ambulance, where I know she's safe.
"There was no concern being shown whatsoever [by the others]."
"Once she said she was assaulted, yeah, the situation just didn't feel right to leave her where she was," King said.
Before leaving the home for the Waipukurau Medical Centre, King said he told the teenager they would be stopping along the way to "make sure she's comfortable" and to check her vital signs.
"We pulled up and stopped ... she said she was still pretty sore," he said.
King claims he then asked the teenager to lift her top to check her ribs, while the girl said the pain was "as bad as before".
"I asked her if she had, had Entonox before."
He said the teen had six big inhales before she said "this is like a massive high".
King recalled the teen then complained of a a sore thigh, which he checked but found no bruising, before taking her vitals again and driving onto the medical centre.
"I stopped for about five to 10 minutes, but you don't look at your watch."
King said his only "concern" was the teens fondness of the gas.
"When I put her on the Entonox and she started huffing it, and said 'this is like a massive high'. That was a bit of a concern. I said 'just use it until your pain was at a manageable level'."
The Crown alleges it is during this stop that King first sexually violated the teen and used his cell phone to record intimate videos.
Upon arriving at the medical centre, King said he entered the back of the ambulance to find the girl with "the mouth piece in her mouth [and] with her head down".
"I pulled it away and gave her a nudge on the shoulder, she gave me a bit of a stare.
"She said something like 'that was a good trip'."
King said the complainant then started uncontrollably screaming "let me out, let me out".
"I thought 'what the?' ... So I opened the doors and let her out. The last thing I wanted to do was grab her as she was running into the medical centre."
He said the teen was screaming "something about an assault", while he tried to simply ask "what's going on?".
The Crown also alleges King again had assaulted and made a second video recording of the teenager in the moments after the ambulance arrived at the medical centre.
The remaining complainants are expected to give evidence during the trial, which Judge Geoff Rea indicated would run until next week.
