The Marine Mammal Stranding Centre, a non-profit group based in New Jersey that rescues and rehabilitates stranded marine mammals, reported the incident on Tuesday.
The aquatic animals, called common dolphins, beached themselves in Sea Isle City, about 50km south of Atlantic City.
The reason for the stranding was unclear.
The deaths come about a week after the group reported that two other dolphins died after washing ashore on a sandbar in Sandy Hook Bay, New Jersey, about 80km south of New York City.
The animals are not considered endangered.
The group said on Facebook that two of the creatures had initially died and the other six were euthanised “to prevent further suffering”.
A veterinary surgeon with the group determined that returning the animals to the ocean would only prolong their deaths.
A representative for the non-profit group was unavailable for comment on Wednesday by telephone or email.