Stress fractures have been found in the stranded ship spewing oil onto New Zealand beaches, heightening the risk of the vessel breaking up, Prime Minister John Key said Wednesday. "We have identified stress fractures on the ship. We can't rule out the risk of the ship breaking up, that's certainly being monitored," Key told reporters. Up to 300 tonnes of heavy fuel has already leaked into the environmentally sensitive Bay of Plenty since the Liberian-flagged Rena hit the Astrolabe Reef, 22 kilometres (15 miles) off the North Island coast, last Wednesday.