If you continue to lose at that rate that would be too fast. The recommended healthy rate is around .5-1 kg a week or 1% body weight.
However it’s common for folks to see a big initial drop. The change in diet, usually less sodium and carbs, causes the body to let go of some of the water it was retaining.
it’s probably water plus your body adjusting to a healthier lifestyle! so much can happen in 7 days, you can even gain/lose a couple of kg overnight! I like to keep one eye on the scale and the other on my body, like how it really looks and feels :) good luck on your journey!