I planted a tomato plant in a nursery bag. The bag's dimensions are approximately 25cm diameter and 40cm height. Is this correct or not? My plants have started to give tomatoes (10 tomatoes per plant every 2 days).
How large a container your tomato plant requires depends on the eventual expected size of the plant. (Tomatoes can grow to be anywhere from 8-10" tall to 10 feet tall or more!) So the optimal size of the container will vary quite a bit from variety to variety.
If you are growing a miniature or dwarf variety of tomato in a regular soil-based system (ie, not hydroponics) then the very smallest pot I'd personally put one of those in would be a 5 gallon pot, which would be a bit larger than the one you say you are using. A ten to fifteen gallon pot would be even better for small to medium size varieties that were expected to grow up to four feet tall during the season. Larger varieties would need even larger pots to stay healthy and produce well. In fact, the most productive potted tomato I ever grew topped out at over 7 feet tall and was actually planted in a (new) 33 gallon plastic trash can.
The bottom line is, your pot is probably too small for the variety you have planted, and if you have a larger pot or other kind of planting container available you might consider transplanting your tomato into it now if the plant is still a manageable size. If you can't transplant it, cross your fingers and be prepared to keep a very close eye on it as it grows, especially in warmer or windy weather.