A spill that sent massive amounts of oil into northern Italy's Po River was a deliberate act of vandalism, officials say.

The officials described the spill as a "criminal act" and said someone opened a valve on an oil tank at a former refinery near Milan.

The oil is expected to traverse the river delta near Venice and flow into the Adriatic Sea within three or four days. However, cleanup teams have been using floating barriers to slow the progress of the oil slick

The Po, Italy's longest river, flows more than 640km from the Cottian Alps to the Adriatic and is connected with Milan by a series of canals.

Al Jazeera's Claudio Lavanga reports.

Source: Al Jazeera