A suezmax tanker off the coast of Peru was involved in an oil spill after it was rocked by waves caused by Saturday's volcanic eruption in Tonga, more than 10,000 km away.

The ship was reportedly unloading when "the violence of the waves" caused a "limited spill", according to a statement from La Pampilla refinery cited by Reuters on Monday.

Media reports and Peruvian authorities said the 158,300-dwt Mare Doricum (built 2009) was involved in the spill.

The ship is owned by Italy's Fratelli d'Amico Armatori and under commercial management of Teekay Tankers, according to databases. It is insured by the Standard Club and classed by Rina.

Fratelli d'Amico said on Wednesday that during a discharge operation, an oil sheen was spotted in the vicinity of the vessel following an "unexpected breakage" of the terminal's underwater pipeline.

The chief officer immediately stopped all discharge operations.

"In coordination with local authorities, anti-pollution measures have since been implemented to contain and minimise any potential environmental impact," the company said.

The Italy-flag Mare Doricum, which is undamaged, is safely anchored off Callao.

Peru's special prosecutor's office for environmental matters, FEMA, said it launched an investigation into suspected ecological crimes against the Repsol-controlled refinery.

The agency cited the fact that the spill appears much larger than initially reported by refinery officials.

"La Pampilla refinery is carrying out coastal remediation and beach cleaning works in the district of Ventanilla after the situation generated by the high tides registered along the coastline due to the volcanic eruption in Tonga," Repsol spokesman Mikkel Larsen said.

"This anomalous situation caused the leakage of crude oil during the unloading process [for the Mare Doricum]."

The spill affected a stretch of Peruvian coastline, including two beaches.

"It is unfortunate. I am seeing that there is a serious impact on the coastal marine area. Initially, two-and-a half-kilometres [of damage] were reported, but now we see that it has affected two beaches," Peru environment minister Ruben Ramirez said, according to Reuters.

The undersea volcano known as Hunga-Tonga-Hunga-Ha'apai erupted on Saturday in what is being called the world's largest eruption in 30 years.

It shot ash, gas and steam 20 km into the air, CNN reported, and was visible from space.

The eruption prompted tsunami warnings in New Zealand, Japan and Peru, as well as on the US and Canadian west coasts.

In Tonga, three people died and homes on several islands were destroyed.

This article has been amended since publication to reflect that the Mare Doricum is commercially managed by Teekay Tankers.