TOKYO—U.S. military forces stepped up relief activities in support of Japanese efforts to cope with a humanitarian crisis.

The 8.9-magnitude earthquake and subsequent tsunami that struck eastern Japan on Friday left thousands unaccounted for and sent more than 200,000 evacuees to relief centers in search of food, water and shelter.

Marines stationed on Okinawa dispatched a high-speed military ferry to Japan Monday morning to assist in the operations, according to the U.S. military. The fast logistics craft, based on a commercial passenger ferry, is to deliver supplies, communications equipment, personnel and equipment for a refueling base.

U.S. Marines continued reconnaissance operations for the planned land-based supply and refueling base, to be set up west of Sendai. "They're going to be building it by today, tomorrow or sometime in the next 48 hours," said Sgt. Maj. Steve Valley, a military spokesman. "So at least then we'll have a supply point close to the major damage."

Aircraft based on Okinawa also took part in the relief operation. According to a Marine Corps news release, two KC-130J cargo aircraft flew to Marine Corps Air Station on Futenma to pick up a command-and-control system and transport it to Naval Air Station Atsugi, Japan. Eight Marine CH-46E transport helicopters are also flying in support of the relief effort.