Updated 2.13pm with Transport Malta statement. 

Transport Malta has launched an investigation into the cause of an oil slick which covered large swathes of the sea at Marsamxett harbour.

It said the oil had leaked from a private facility on Manoel Island and it would investigate why it was not contained immediately. 

Video footage and photos sent to Times of Malta on Tuesday showed oil appearing to wash into the sea from the Manoel Island Yacht Yard and stretching across to Tigné.

When contacted, reception staff at the yacht yard said its management were “in a meeting” and unavailable to speak to the media, but would decline to comment.

On Wednesday morning, the Environment and Resources Authority (ERA) said it had confirmed the spill was "used oil" and that a cleanup had begun using specialised equipment.

A small bay near Tigné was closed off for health reasons.

Photographs from the area taken on Wednesday showed that a lot of oil remained in the sea, but Transport Malta said the slick would be cleared by later in the day. 

Aerial footage and photos of the area showed the oil – indicated by its rainbow-coloured appearance (known as ‘thin-film interference’) – appearing to seep from a part of the yacht yard filled with industrial equipment, rubble and numerous liquid containers.

The images showed dark marks on the ground in the yard appearing to run into the sea.

The oil stretched across the fairway amid scores of boats moored close to Manoel Island.

Other footage provided by NGO Żibel appeared to show staff implementing measures used to contain oil spills on Tuesday evening on the Tigné coastline.

Commenting on footage of maritime staff in the area on Tuesday evening, Schembri said it was good to see oil spill protocols being implemented, explaining that under such circumstances it was normal that a boom was set up to contain the spill.

Initial investigations suggest the oil spill came from Manoel Island. Photo: Steve Payne

He however slammed authorities for the delay in publishing information about the spill, saying a lot of people swim close to that place every day.

He said members of the public also reached out to the NGO because the oil had leaked for several hours and nobody had done anything about it.  "Someone should be held accountable,” he insisted

Photographs taken on Wednesday show oil remains in the area.

Transport Minister Chris Bonett said an investigation was ongoing to determine how similar incidents could be avoided. 

Asked if those steps would include fines Bonett said:

"There are several steps we can take but I cannot speculate what they will be if I don't know what caused the spill or if there was any negligence".

He said marine oil spills are rare in Malta "but one accident is one too many".

The area around Tigne where swimming has been banned.