A Washington state senator was arrested at a Hong Kong airport on charges of possessing a locally unregistered firearm, his office said on Monday.

Jeff Wilson, a Republican who represents parts of southwestern Washington State, discovered the weapon on his flight from San Francisco to Hong Kong when he reached into his briefcase for a piece of gum, his office said in a statement.

Baggage screeners in Portland, Ore., had failed to notice the unloaded pistol in his briefcase before he departed for his trip, letting it pass through airport security, according to his office. When he landed at Hong Kong International Airport, he told customs officials there about the gun.

Mr. Wilson was arrested on Friday night, then released on bail on Sunday, his office said. His next court hearing is next Monday.

“It was an honest mistake,” Mr. Wilson said in the statement. “I expect the situation to be resolved shortly.”

The Transportation Security Administration, which manages passenger screenings at U.S. airports, did not respond to emailed requests for comment on Monday night. Hong Kong’s Customs and Excise Department declined to comment on Mr. Wilson’s arrest, saying that the legal proceedings were underway.

Mr. Wilson, who was elected to the Washington senate in 2020, has sponsored legislation that made it easier for museums to receive guns from firearm collectors. The bill passed this year.

According to the statement from his office, the pistol was properly registered in Washington, and Mr. Wilson held a concealed-pistol license although the gun was unregistered in Hong Kong.

Mr. Wilson had started a five-week personal vacation with his wife, his office said. He hoped to resume his planned travel to Thailand, Cambodia and Malaysia once the matter in Hong Kong was resolved.

Under Hong Kong’s laws, carrying firearms without a license is punishable by up to 14 years in jail and a fine of up to 100,000 Hong Kong dollars, or about $12,800.

In the United States, officials have raised alarms about the growing frequency of guns at airport security checkpoints. Passengers can travel with unloaded firearms in checked baggage if they are locked in hard-sided containers. No guns are allowed in carry-on bags at any checkpoint, even if the passenger has a concealed-weapon permit.