One of the key problems slowing recovery efforts for millions of desperate Puerto Ricans still without power and water: the challenge of distributing fuel and supplies already on the ground.

In many parts of the island of 3.4 million people, the recovery in the first weeks after Hurricane Maria has largely been a make-it-up-as you-go-along affair, particularly for those still cut off by blocked roads and unable to communicate to the outside world.

People collect water from wells and streams, clear roads and repair their own homes when they are not waiting in daylong lines for gasoline and diesel. For most, the only visible signs of authority are police officers directing traffic, a critical service because traffic lights are out across the island.

“I have seen a lot of helicopters go by. I assume those are people from FEMA,” said Jesus Argilagos, who lives in Manati and works at a grocery store that is only open part of the day because of the power crisis, the Associated Press reports. “People get pissed off because they see them going back and forth and not doing anything.”

San Juan Mayor Carmen Yulín Cruz, breaking down during one TV interview, says people on the island are in a “life and death” struggle." More than a million people lack drinking water and most of the island is without power.

“I know that leaders aren’t supposed to cry and especially not on TV, but we are having a humanitarian crisis," Yulín Cruz told WUSA-TV. “It’s life or death, every moment we spend planning in a meeting or every moment we spend just not getting the help we’re supposed to get, people are starting to die.”

But getting supplies from Point A to Point B remains a daunting task in a country still battling to open roads or even get out from under standing water.

"We are well aware of the fuels needs on the ground," FEMA deputy administrator Daniel Kaniewski told CNN. He says there is "sufficient fuel" in depots, but "the challenge we have quite frankly is distributing it."

Likewise, Gov. Ricardo Rosselló tells CBS News that emergency administrators are running out of truck drivers to bring supplies to groceries and distribution centers. They are now looking for bus drivers and others with commercial licenses to go to the port in San Juan to help get the materials out.

CBS reports that 3,000 shipping containers packed with food, water and medicine have been sitting at the port in Puerto Rico since Saturday.

The governor does note progress, however slow, in some areas. Rosselló said Tuesday that 450 of the island’s 1,100 gas stations are now working, up from 181 two days earlier, The New York Times reports.

The Trump administration said Tuesday that it was sending a flotilla of ships and thousands more military personnel to Puerto Rico to address the growing humanitarian crisis caused by Hurricane Maria.

Brock Long, administrator of FEMA, acknowledged Wednesday that the devastation wrought by the storm presented logistical challenges, and badly damaged airports and seaports are making it difficult to get aid and personnel to the stricken island.

Long said 16 Navy and Coast Guard ships were in the waters around Puerto Rico, and 10 more ships are on the way. They include the USNS Comfort, a Navy hospital ship based at Naval Station Norfolk. Planes and ships were also bringing in a military force numbering in the thousands to help distribute aid. Military aircraft were dropping food and water to areas of the island still isolated and unable to receive help by road, he said.

“We’re dramatically increasing the federal footprint that’s there,” Long said, speaking outside the White House.

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Gen. Joseph Dunford, chairman of the Joint Chiefs, said the priority is making sure that airfields are operational.

"All the other support they need can't come in until we get the ports and airfields open, so that's why Northern Command has placed that at the top of the list in terms of the support we're providing," he said on Capitol Hill, according to CNN.

Dunford said he expects more military aircraft will be used particularly for "generators, water, food, those kind of immediate needs."

Meanwhile, flights to and from Puerto Rico continued to improve Wednesday. Most are relief efforts; others are commercial passenger flights. The Federal Aviation Administration has restored most radar and surveillance equipment to track planes and re-established radio frequencies between the islands and the control center in Miami that guides planes between airports, according to Greg Martin, an FAA spokesman.

“It’s a very extraordinary situation,” Martin said. “The situation improves by the minute.”

FEMA and the Defense Department, which are coordinating relief flights, set a limit of 36 takeoffs and landings per hour on Wednesday, up from 28 per hour on Tuesday and 18 per hour on Monday, Martin said.

The total number of flights was 331 on Tuesday, 328 on Monday, 252 on Sunday, 191 on Saturday and only 22 on Friday, Martin said.

Among those Wednesday flights were 19 by commercial passenger airlines, up from 15 on Tuesday, Martin said. Commercial airlines aren’t yet using all the slots allowed because they must demonstrate to FEMA that they can handle the ground operations such as ticketing and screening in a damaged terminal.

“We have the air capacity restored that we can handle flights, both relief and commercial,” Martin said.

Several thousand U.S. federal employees are in Puerto Rico helping with the recovery effort, most visibly in San Juan, the capital.

Officials from FEMA, Homeland Security, Customs and Border Protection have a presence at tourist hotels or at the convention center that has become a staging ground for relief efforts.

Federal workers have supplied diesel to generators to hospitals and delivered desperately needed food and water to hard-hit communities across the island. They have also repaired the air traffic control systems and power at the airport, which is far from normal operations with only about a dozen commercial flights per day.

In addition, U.S. agents have provided security across the island while the Coast Guard has worked with local authorities to restore the seaports, a vital link for an island almost completely dependent on imports.

In addition, teams from the Army Corps of Engineers are helping to repair the electricity grid and to inspect and look for ways to avert the collapse of a dam near the western town of Quebradillas that has developed a crack.

Teams are scheduled to visit the central mountain town of Aibonito, which was cut off from the rest of the island for five days. Many people began rationing their food and water supplies as they dwindled, unclear when they would have contact with the outside world, the Associated Press reports.

Contributing: Bart Jansen, in McLean, Va., Associated Press