MYANMAR, Yangon (CNN) -- A Red Cross boat delivering supplies to help 1,000 victims of last weekend's cyclone sank Sunday when it hit debris in the Irrawaddy Delta region, as the U.S. prepared to deliver relief supplies to Myanmar.

"The crew managed to get to the safety of an island, along with four Red Cross staff who were on the boat," Red Cross official Joe Lowry said. "But we've lost most of the cargo."

The double-decker relief boat was carrying about 100 bags of rice, 5,000 thousand liters of drinking water, 10,000 water purification tablets, 200 water storage containers, 10 stretchers, 30 boxes of clothing and household items like soap.

A submerged tree damaged the hull of the boat as it headed toward the delta township of Bogalay, which was hit hard by the cyclone, Lowry said. The boat sank quickly, leaving its cargo at the bottom of a muddy river, he said.

The boat was traveling from Yangon to Mawlamyinegyun when it sank, according to the Red Cross.