A typhoon that slammed into Guam, knocking out power and flooding buildings with a powerful storm surge, was moving away Thursday – leaving residents of the US Pacific Ocean territory to survey the damage.

Governor Lou Leon Guerrero was set to venture out when conditions allow to see what damage has been wrought on the island, a key US military outpost and home to 170,000 people.

The governor and civil defence groups will look for "any major damages or blocked roadways in the wake of Typhoon Mawar," a statement said on Thursday.

"As Guam received the full brunt of the typhoon overnight, the assessment will help determine what damages may have occurred."

Mawar brought winds of up to 225 kilometres an hour, the US National Weather Service reported, generating waves nine metres high. There were no reported deaths or injuries.

At one of the island's many hotels, the 30-floor Dusit Thani Guam Resort housing about 300 guests, desk clerk Casey Hattori said the lobby was inundated with a foot of water, even with the front door barricaded with boards and bags of concrete. Outside, trees snapped in howling wind.

"I can hear the walls shaking. The wind is super strong. I can hear it whistling as it comes through the cracks of the doors," Hattori said.

Fearful tourists were evacuated from flooded rooms to a sixth floor ballroom, she said. (AFP)