Fishermen, volunteers and Philippine Coast Guard personnel all joined hands to assist the estimated over 330 melon-nosed dolphins stranded in Bataan province near the capital Manila on Tuesday.

Bataan Gov. Enrique Garcia, Jr. said residents in Mariveles, Bataas first reported seeing the huge number of beached dolphins at around 2:30 am.

Volunteers from the community, aided by experts from the PCG and Bureau of Fisheries and Aquatic Resources, rushed to the scene and tried to guide the dolphins into the open seas. However, the dolphins refused to leave the shallow waters, volunteers say.

At around 12 noon, the dolphins were finally guided to the open seas, but residents in Hermosa near Mariveles were surprised to see the dolphins near their shoreline.

So the PCG, BFAR and fishermen rushed to Hermosa to again guide the dolphins back to the open sea as the situation is already dangerous for them.

At around 3:30 pm, all the dolphins have left the shoreline and swam towards the high seas. However, three dolphins died, including a female pregnant dolphin.

Authorities were surprised by the sheer number of dolphins stranded in the province. It was not uncommon in the Philippines for dolphins and whales to be stranded in shallow shorelines, but this is the first time that over 300 were beached at the same time.

BFAR director Malcolm Sarmiento said authorities will investigate the stranding of the large numbers of dolphins. One theory being floated is that the mammals may be reacting to a "heat wave or disturbance at sea" such as a possible major underwater earthquake.

Another suspicion is that the leader of the pod was injured and the entire school followed the dolphin near the shallow waters.