RIO DE JANEIRO (AP) — Around 30 large dolphins beached themselves in northeastern Brazil over the weekend, and news reports said Monday that at least seven of them had died.

The dolphins, known as false killer whales, ran aground early Sunday on the shallow sands of Upanema beach in Areia Branca, roughly halfway between the cities of Fortaleza and Natal.

Images distributed by the environmental police of Rio Grande do Norte state show beachgoers and passers-by attempting to aid the animals, which lay stranded in inches- (centimeters-) deep water. Most of the animals were still, occasionally twitching their tails, as beachgoers swabbed them with wet T-shirts.

O Globo newspaper reported Monday that at least seven on the animals died, six of them on the Upanema beach. O Globo said one animal died following an apparent shark attack after it was returned to the ocean. The report stressed that the dolphin was likely attacked in very deep waters and that area beachgoers needn't worry about shark attacks.

The paper said it was not immediately known why the animals beached themselves, but biologists were examining whether the pod leader might have been ill. Another hypothesis is that the dolphins were pursuing a school of fish and were trapped on Upanema's high sand banks.

O Globo said it was among the largest collective beachings in Brazil in recent decades. In 1991, around 19 whales beached themselves on the sands of the nearby town of Sao Miguel do Gostoso, the report said.