The military is sending a three-star general to Puerto Rico to coordinate ramped up relief efforts as Democrats urge wider assistance to the devastated U.S. territory, U.S. Northern Command said Thursday.

The decision comes just a day after Northern Command sent a one-star, Brig. Gen. Richard Kim, to the island to set up a headquarters and work with the Federal Emergency Management Agency and Puerto Rican authorities on rescuing residents, delivering food and water, and restoring power.

Now, Lt. Gen. Jeffrey Buchanan, commander of U.S. Army North and Kim's boss, will take over coordinating those operations as more military cargo flights arrived on the island Thursday and the Navy hospital ship USNS Comfort was preparing to start its voyage there.

The arrival of Army generals also indicates the military's shift from an initial relief effort from the sea to a longer-term, land-based recovery operation. The previous highest ranking officer in the area was a Navy rear admiral, according to Northern Command.

Democrats on Capitol Hill have criticized relief efforts for the territory's 3.4 million American citizens as inadequate and 145 House members sent a letter to President Trump Wednesday urging him to send the USS Abraham Lincoln aircraft carrier and a top general.

Sen. Bill Nelson, D-Fla., a member of the Armed Services Committee, wanted to know "where the hell is the cavalry" on Thursday and said that aid was still not reaching victims of Hurricane Maria, which raked across the island last week after an earlier hit by the powerful Category 5 storm Hurricane Irma.

"There is a crisis in Puerto Rico where food, fuel, water, and medicine is sitting at the docks and not getting out to the remote parts of the island," Nelson said. "The situation calls for an immediate response by the U.S. military to provide security and distribution to these remote areas."

The Navy sent a group of ships loaded with Marines in the wake of the storm to help rescue residents, drop supplies, and open airports and seaports. That was followed by deployment of Black Hawk helicopters and cargo flights with relief supplies.

On Thursday, a military C-5C Galaxy delivered a FEMA generator that will help increase the number of flights at San Juan's international airport and two C-17 Globemaster cargo aircraft arrived with a mobile medical unit and with Federal Aviation Administration personnel to support air operations, according to Northern Command.