SINGAPORE - A seaman with the United States Navy is said to be missing in Singapore for almost two days.

Seth Woods was last seen at a 7-Eleven store, a person claiming to be his cousin said on Internet forum Reddit Singapore on Monday (May 7).

"He and a friend got off the ship in Singapore," wrote the user jms428.

"His friend went to 7-Eleven and he went to a smoking area to vape. When his friend came back he was gone. It's been over 30 hours. They called his mother this morning. Just sharing for awareness and the hope he is found."

Lt Commander Arlo Abrahamson, the US Navy's spokesman for the US 7th Fleet in Singapore, told The Straits Times on Tuesday night that the navy was aware of the situation and is looking into the matter.

"The US Navy is cooperating with local authorities and we will continue to diligently search for this missing sailor," he said.

Seth is 18, his sister Ms Jodi Brown told ST.

She posted photos of her brother in uniform and civilian clothes on Facebook, asking anyone who has seen him to contact her.

In a post on Tuesday she wrote: "My brother is currently missing in Singapore... so if anyone hears from him please let my family know... We don't know much information but his shipmates are looking."

Ms Brown told ST that she had no reason to believe that he deliberately ran away.

"He loved what he did," she said. She did not know where he was last seen, except that it was at a 7-Eleven store. It is unclear which outlet it was.

Seth's mother told ST that she was told about his disappearance on Monday morning.

"The navy is all out looking for him," she said. "He has not been in contact with us. The last time I heard from him was March 17, just before he left."

"I wish I knew more, it's killing all of us here feeling helpless because I can't do anything," she said.