Fear & Anxious. Help, really worried.

My 4.8 years old daughter is very fearful & anxious to talk to people other than parents, grandparents, few of her friends & very few others. She will not interact with anyone outside house even in parent's presence and even if someone come home she will​ not talk to them. She will just stay with us if outside without going away and if at home if someone comes she might walk around after a while but fail to talk to the visitors. She don't talk to her teachers much even in our presence. She also refuse to play with kids other than very few selective friends. She don't go out with her friends to classes that we have in our apartment like drawing, swimming etc. If given confidence by talking to her she will go till there and stay there stuck without going inside or talking and if asked what happened she will simply stand with tears from her eyes without saying anything even to us. If she is taken back home she has no problems & start playing immediately. Please help, really worried.