Somewhere I read that 'This container contains highly flammable petrol '. This particular instruction is written in my native as well as in the English language. My confusion arose when I was going to convert the sentence from my native language to English. I thought that it should be extremely rather than highly. I also found that both have the same meaning in my native language.
Can anybody tell me the difference between highly and extremely? When should I use each one? (Please give examples)