A US beach town was advising against ocean swimming after two youths were mauled by at least one shark last weekend.

A 12-year-old girl from Asheboro was bitten so badly near an Oak Island pier in North Carolina last Sunday that she lost part of her left arm and suffered a leg injury.

About 80 minutes later and two miles away, a shark bit off the left arm of a 16-year-old boy from Colorado Springs, Colorado.

Dr Borden Hooks operated on both victims. He said the boy was awake and talking to doctors, but the girl’s family had asked that no more updates be provided.

Both were later reported to be in a good condition.

Florida shark researcher George Burgess said he is aware of only two other multiple shark attacks on the same beach in one day.

Mayor Betty Wallace told Reuters that said shark encounters are virtually unheard of there, adding that a long-time resident could not recall a single one in 36 years.

“I don't want everybody to think this is one of those areas where you really have to worry about shark bites,” she said. “But for the foreseeable future, people have to be extra vigilant.”