HOBOKEN, N.J. — National Guard troops delivered food and water to residents in this heavily flooded city across from Manhattan on Wednesday as officials sent out a plea for more supplies, including boats and generators.

Superstorm Sandy sent the raging Hudson River waters from one side of the one-square-mile city to the other Monday. Two days later, at least 25 percent of the community was flooded and 90 percent was without power, leaving many residents increasingly anxious and municipal leaders struggling to get assistance to all those who need it.

Tempers flared Wednesday at a staging area outside City Hall, where a man screamed at emergency officials about why food and water had not been delivered to residents just a few blocks away. The man, who would not give his name, said he blew up an air mattress to float over to the staging area.

City officials defended their response.

“The dimension and scope of this situation is enormous,” Public Safety Director Jon Tooke said. “You have emergency operations at all levels — from local to federal — spread too thin across the city and the state, but we’re working on it.”

Tooke said the estimated 20,000 people still stranded in their homes were being encouraged to shelter in place, and that high-water vehicles would get supplies to them. He said people with medical and other special needs were being taken out by trucks. Two churches were serving as shelters.

Public housing, senior projects and private residences were all affected. Mayor Dawn Zimmer said senior citizens were the most distressed and eager to get more supplies.

National Guard troops in 12 trucks arrived Tuesday night, officials said. On Wednesday the city appealed for additional aid, including boats and generators. Zimmer asked local businesses to get water and nonperishable goods to City Hall.

“We are doing what we can but we really need more help,” said her spokesman, Juan Melli.

Dozens of volunteers answered the call to help go door to door to see if seniors and others needed water or other supplies.

Frank Bongiorno, an 80-year-old resident of a senior high-rise, said he walked down 15 flights to get out of his building, then waded through some low water to get to City Hall.

Wearing a sweatshirt too thin for rapidly dropping temperatures, Bongiorno said he needed to get out. “They finally gave us a sandwich today but it was this big,” he complained, pinching his fingers about an inch apart. Tooke said fuel had been delivered to the high-rise to get its generator back up and running.

Many were surprised by the extent of the flooding.

Samuel Scott Cornish, 34, who lives with his wife, Katie, and newborn son, Jack, in a luxury apartment complex on the border of Hoboken and Jersey City, said he was told to move his Subaru to a different area inside his building’s garage for safety before the storm, only to later discover it floating in water. The garage is now filled with water-soaked cars, including a BMW floating upside down.