Great Britain's Jonathan Fox set a world record - the first of the Paralympic Games - in the men's 100m Backstroke - S7, winning his heat in 1:09.86.
He said: 'Coming into the heat I was looking to qualify first for the finals, which I've rightly done.
'I didn't know it was a world record until I looked up at the screen. I've wanted to go under one ten for a long time. What a great way to start the competition.'
Ukraine's Kateryna Istomina set a world record in the women's 100m Butterfly - S8 and Sophie Pascoe of New Zealand also did so in the women's 200m Individual Medley - SM10
Jaqueline Freney of Australia set a Paralympic record in the women's 100m Backstroke - S7.
Great Britain's Nyree Kindred booked her passage into tonight's in the S6 100m Backstroke final in a Paralympic record 1:27.96 seconds, lowering by 0.22 the mark set by China's Lu Dong in the first heat.
London 2012 is the 32-year-old's fourth Paralympics and she is looking to add to the nine medals, including two golds, she has already secured.
The Great Britain swimmer said: 'I couldn't ask for anything better in a heat swim. I would like to go quicker; that was a hard race so I am going to try with the crowd with me.
'But anything could happen because all those girls who made that final are capable of a lot more so you've just got to watch this space and see what happens.'