Trump tweets about 'amazing' FEMA response in Puerto Rico but locals say 'still waiting' for aid Most of the island is without electricity and half of residents lack water.

 -- Amid mounting criticism, President Donald Trump took to Twitter on Thursday night to defend the federal government's response to the disaster in Puerto Rico after Hurricane Maria devastated the island.

Trump wrote that the Federal Emergency Management Agency (FEMA) and first responders were "amazing" and doing a "great job."

But residents of Puerto Rico and outside observers have taken the government to task for what they see as delayed or insufficient action after Maria, the strongest hurricane to hit the island in nearly 90 years.

Maria blasted through on Sept. 20, killing at least 16 people, knocking out power to nearly all of the island's 3.4 million residents and leaving half without potable water. Communications on much of the island were also knocked out amid widespread damages that officials say could take months to repair.

ABC News' Eva Pilgrim reported from the capital San Juan on the humanitarian crisis eight days after Maria struck, as residents waited in line for dwindling water supplies and trucks with gas and supplies struggled to reach residents.

San Juan Mayor Carmen Yulin Cruz told Pilgrim, "I'm not waiting. I'm not waiting [for federal aid]. I'm working with what we have."

Pilgrim and ABC News' Joshua Hoyos reached the storm-ravaged Vieques, an island municipality of Puerto Rico just seven miles away, where they found "no power, no running water" and a hospital "so severely damaged that it has been forced to set up a temporary triage tent outside to treat patients."

"Just waiting, we're still waiting," a doctor at the hospital said, adding that FEMA has only delivered water so far.

Trump came under fire this week for tweeting about NFL player protests and Puerto Rico's "broken infrastructure & massive debt" as the island faced what Gov. Ricardo Rossello called "probably the single biggest hurricane catastrophe in the history of the U.S.”

GOP Sen. Marco Rubio wrote a letter to Trump asking him to improve the government's response to the devastation in Puerto Rico. Rubio, who has sent staffers to the island, requested that the Defense Department be put in charge of handling the logistics of distributing aid across the island -- given the pressing issue of accessibility and moving relief from the ports to inland communities.

Trump administration Homeland Security officials also faced a backlash over their response to a request to waive the Jones Act, a near-century-old law that requires all goods shipped to the island travel on vessels owned and operated by Americans.

Officials in Puerto Rico claimed the law was hindering aid and eight members of Congress sent a letter to the Department of Homeland Security asking for the waiver to be granted, as was the case in Texas and Florida following Hurricanes Harvey and Irma.

Following a request from the governor of Puerto Rico, Trump said his administration was "thinking about" waiving the law on Wednesday.

Ret. Lt. Gen. Russel Honore, who was called in to turn around the response to Hurricane Katrina by then-President George W. Bush, said the delay in issuing the waiver for Puerto Rico was "a crying damn shame," in an interview on CNN that same day.

On Thursday, White House press secretary Sarah Huckabee Sanders announced the waiver was being granted at Gov. Rossello's request.

ABC News' Benjamin Siegel and Lucien Bruggeman contributed to this report.