A hotel in Guam has been evacuated after an explosion that left two people injured.

The explosion went off at about 8.30 pm local time Thursday, near the outdoor Tree Bar at the Hilton Resort and Spa in Tumon, on the west side of the island.

The Guam Police Department has confirmed the explosion did occur and says an investigation is underway.

Police Sergeant Elizabeth Flickinger says the FBI, Homeland Security and Office of Civil Defence as well as the Bureau of Alcohol Tobacco Firearms and Explosives are on the scene.

She says the agencies are monitoring the area and waiting until daylight to further the investigation.

"As far as what caused the explosion, that's not yet known," she said.

"What's left at the scene is a large crater from the blast."

Hotel manager Makoto "Earnie" Yasuhara says staff had begun evacuating the building before police arrive, but they have all returned to their rooms.

"Two of our guests had a minor injury because of the explosion," he said.

"Under the directions from the police we evacuated the entire hotel for the safety of the guests."

Two people were taken to Guam Memorial Hospital with minor wounds from the blast, but both have been treated and released.

The Guam Fire Department says the two were a 32-year-old male Japanese tourist and a 33-year-old local female.

Japan's foreign ministry confirmed that a Japanese man was slightly injured.

Guam Delegate Madeleine Bordallo has issued a statement sending prayers to the victims.

"I extend my thoughts and prayers to the two individuals who were injured during this incident," she said.

"I appreciate the efforts of federal officials who are on-scene providing assistance to local authorities. I also appreciate the efforts of our first responders who were on the scene immediately following the incident.

"As we await further details on the cause of this explosion, I will continue to work with federal officials to ensure appropriate federal resources are brought to bear during this investigation."