Colombo, Sri Lanka (CNN) -- Aid workers scrambled to help more than a million people in Sri Lanka suffering from massive flooding described by the government as the worst natural disaster since the 2004 tsunami.
At least 23 people have died and 36 others were injured in the destruction wrought by torrential rains, the Disaster Management Center said.
The Sri Lankan government and United Nations agencies were beefing up efforts to address increasingly dire humanitarian needs.
"We share the strong concern over the immediate requirements of over one million affected, especially the most vulnerable including children," said Neil Buhne, the U.N. humanitarian coordinator in Sri Lanka.
He said the global body was already looking at longer-term effects from damage to agriculture, infrastructure and housing. About 125,000 acres of the nation's staple rice crop has been destroyed, the government estimated.
The full extent of the damage cannot be assessed until flood waters in northern and central provinces recede, but Mahinda Amaraweera, minister of Disaster Management, told a news conference the losses were severe.
So far, he said, the government has allocated more than $1.5 million for recovery efforts and prompted the largest military response since the 2009 defeat of the Tamil Tigers. More than 28,000 troops, backed by transport helicopters and navy boats, were engaged in rescue and food delivery operations.
Many of the people in flood-affected areas are still recovering from the 25-year bloody conflict between the government and the rebel Tamil Tigers.
George Sigamoney, secretary-general of the Catholic charitable organization Caritas in Sri Lanka, said it has been difficult to access places affected by overflowing rivers, broken dams and drowned roads.
"Hundreds of farmers had started to cultivate their fields again after the war," he said on the Caritas website. "But these efforts are turning to be futile as the rains continue to lash the rice growing areas. A lot of houses from our shelter programs have been damaged in the floods as well."
The U.N. World Food Programme said it was "facing major breaks in food supplies." It said rations for people returning home after the war has been significantly reduced since October.
Sigamoney feared more misery lay ahead with shortages and exploding prices of basic food items.
"The poor will find it even more difficult to afford the most basic food items", he said.
Journalist Iqbal Athas contributed to this report.