My daughter is a biter

I have a problem and i have no idea how to deal with it.

It started about 5 weeks ago, my daughter who (im not being biased) has always been a well behaved child, has started biting other children at nursery. It has got to a point now where its at least once every time she is there. she only goes to nursery twice a week and everytime i go to pick her up the nursery informs me that she has biten another child.

i really dont know how to tackle this one. They keep saying its a fase that she will grow out of but its awful. they have phoned me today to tell me that she has bitten another 2 children this morning and bruised one of them by biting on there face :0 im mortified!!

It started as slapping and has progressed onto this. At home she dosent bite, she does on a rare occasion try to bite but i notice straight away when she is about to do it and tell her "Dont bite" and she stops immediatly.

any one else ever had to go through this? im confused on what to do