A ship carrying more than 70 passengers and crew sunk off Indonesia's Sumatra island on Thursday amid bad weather, a naval spokesman said.
The accident occurred around 64 kilometres off the port of Sibolga on western Sumatra, Lt Col Jaka Sentosa told el-Shinta radio station.
Rescue vessels were heading to the scene, but were being hampered by large waves, he said.
"The information we have received is that the boat sprang a leak and that the weather was very bad," he said.
Sentosa said at least two foreigners, reported to be US citizens, were on board.
He said he had received a report that a passing ship had picked up some survivors, but could not confirm it.