Updated Thursday 12.30pm

A diesel spill was seen at the Grand Harbour on Wednesday, with people on Facebook saying it could have been the result of Tuesday's boat fire.  

A motor cruiser burst into flames while berthed in Kalkara, sending thick black smoke into the sky. The yacht damaged nearby boats, causing tens of thousands of euros in damages.

Watch: 'It was like a fireworks factory exploded'

The cause of the incident is not yet known. The fire died when the boat started sinking.

Photographer Rene Rossignaud said the spill could be seen from Kalkara bay all the way to the breakwater.

ERA compliance officers immediately carried out investigations on site upon being alerted to the case, concluding that it was all probability related to the yacht fire.

The ERA said it was in contact with Transport Malta, which is the competent authority for cases of spills within the Grand Harbour, and with the Civil Protection Department, who are all also following the case.

"The thin sheen visible on the sea surface cannot be removed and will normally dissipate naturally within a day or so. That being said, kindly be informed that the sunken wreck, which may still contain some diesel residues, cannot be recovered for the time being in view of ongoing court investigations and certain interventions by the competent Authorities can only be taken with court clearance," the authority spokesman said.