Peru's National Maritime Authority has launched an investigation amid furore over an oil spill blamed on waves from a volcanic eruption in Tonga.

The move comes after what was initially thought to be a minor spill in waters off the Lima suburb of Ventanilla has ballooned into what President Pedro Castillo has declared an environmental emergency.

The country's navy said the probe will aim to seek the causes of the incident and determine the responsible parties.

The maritime authority, which is part of the navy, will “scrupulously follow” legal norms in the investigation with the “aim of avoiding speculation”.

As TradeWinds has reported, the spill took place on Saturday evening at the La Pampilla refinery, operated by Spanish oil giant Repsol, while Fratelli d'Amico Armatori's 158,300-dwt Mare Doricum (built 2009) was unloading a cargo of crude.

The Italian shipowner has said the spill followed an “unexpected breakage” of the terminal's underwater pipeline.

Some 6,000 barrels of oil are believed to have spilled in the incident, leading to blackened beaches and oily seabirds.

The navy said it “laments the damage caused by this incident, which has gravely affected the ecosystem and maritime natural resources”.

On Thursday, Castillo signed a decree declaring an emergency while visiting some of the coastline impacted by the spill, describing it as the most troubling ecological disaster in recent years.

“We are going to lead actions to mitigate the damages, for which a crisis committee will present concrete actions in the next few hours,” he said.

Peruvian officials have pointed the finger at Repsol for the spill, demanding compensation and complaining that the company initially under-reported the severity of the incident.

But Repsol has said in media reports that it is not responsible for the spill, caused by a tsunami that started some 10,000 km away.

“The oil spill was caused by a maritime phenomenon unforeseeable by the company as a result of the volcanic eruption in Tonga,” Repsol said in a statement, according to Upstream.

Mirtha Vasquez, the president of the government's Council of Ministers, told reporters the oil company could face administrative sanctions from Peru's Organisation of Environmental Evaluation and Inspections, according to El Comercio newspaper.

But Repsol told securities regulators in Peru that the body, known by its Spanish acronym OEFA, has not informed it of any administrative process that could lead to sanctions.

The Mare Doricum remains at anchor off the Peruvian coast, according to tracking data from VesselsValue.