Beachgoers in the Gulf Coast of Florida have been told to be vigilant, after three swimmers were attacked by sharks in two separate attacks.

One woman was said to have had part of her arm amputated after being bitten on Friday in Walton County in north-west Florida.

Less than two hours later, at another beach four miles further east, two teenage girls were in waist-deep water with friends when they were attacked.

One of the girls suffered “significant injuries to the upper leg and one hand” while the other had minor injuries on one of her feet, fire officials said.