Samsung is delaying shipments of its new Galaxy Note 7 smartphones to investigate reports of exploding batteries.
"Shipments of the Galaxy Note 7 are being delayed due to additional tests being conducted for product quality," Samsung said in a statement.
The firm did not elaborate on what potential problems it was testing for or whether shipments to other countries were being affected. South Korean media reports have said some users have claimed that the battery exploded.
Quality control problems could deal a major blow to the world's top smartphone maker, which was counting on the Galaxy Note 7 to help maintain sales momentum in the second half when competition is expected to intensify.
The device was released in Australia and other markets on August 19.
Production problems for the curved displays for the Galaxy S6 edge phone resulted in disappointing sales last year, and Samsung risks a repeat this year if it cannot address the Galaxy Note 7 supply problems quickly. Rival Apple is expected to unveil its new phones next week.
Samsung has said demand for the new phone is far exceeding supply, creating a shortage and forcing it to push back the launch in some markets. The firm has said it is utilising all possible means to boost production.
Samsung's other premium smartphone models that launched in March, the Galaxy S7 and S7 edge, have been huge hits with customers and lifted earnings in the first half.