The tanker was stranded last month near Karachi harbour, and is still holding around 32,000 tonnes of crude oil after about 12,000 tonnes had already spilled out of the ship causing a massive loss of wildlife.

Three attempts were made to tow the tanker away before its hull broke open on Wednesday and oil began oozing out.

Salvage and pollution control experts from Holland, England and Greece were assisting Pakistani authorities, which were using booms to prevent crude from entering the port waters.

Pakistan, which is poorly equipped to handle the crisis, is importing pollution control and salvage equipment from various countries while neighboring India has also offered assistance.

Officials said they were still hoping to transfer some of the tanker's cargo to another ship, but agreed it was difficult to tell how soon it would be safe to do so.

The incident has unleashed fresh criticism of Pakistan's level of preparedness in dealing with marine accidents, especially around Karachi, home to the main operational establishment of the Pakistan navy and other maritime organisations.