At least 264 dead bottlenose dolphins have washed ashore over the past three days on Peru's northern coast, officials said as they seek to discover what killed the marine animals.

The dead dolphins were found over a 103 kilometre stretch of sandy beach, said Edward Barriga, an official with Peru's Oceanic Institute (IMARPE).

"We have taken samples to determine the cause of death," said Barriga, speaking from the city of Lambayeque, adding that vast quantities of dead anchovies had also been found in the region.

The dolphins may have been killed by the impact of off-shore oil exploration and drilling in the region, said Carlos Yaipen with ORCA, a non-governmental group that focuses helping ocean creatures in the south Pacific.