"The situation is terrible - over 150,000 have fled Abyei and the areas around," said humanitarian affairs minister James Kok Ruea.
Northern troops took control of the contested border region, also claimed by South Sudan last week. The area is due to become independent in July, but world powers now fear the action threatens to reignite the north-south civil war in which some 1.5 million people died.
"Women, children, elderly - they are running in fear from brutal violence, without shelter," Ruea said.
The number of people now homeless in the north eastern African country is a big rise from the earlier United Nations estimates of between 30,000 and 40,000.
Alel Bol fled her Abyei home with four of her six children when armed northerners on motorbikes surged into the region and she said, bombs started falling.
"I saw the attackers ... I saw their guns. They were even bombing from the sky," she said. "I made it here with four of my children, but two are missing," she told Reuters news service.
Today she was still waiting for news about what had happened to her other two children.
Similarly, Deng Niwol, 14, fled his village south of Abyei when he heard the gunshots. "No one is left in the village. My family was eleven people. Some are here, some are not yet," he said.
They and tens of thousands others sought safety in villages inside south Sudan, many of them sleeping outdoors under trees, plastic sheets and torn fabric.
"The situation is going from worse to even worse,” said Dominic Deng, commissioner of Twic county. "They need food and water ... some people are dying."
He said that about 80,000 people had fled Abyei since the fighting started. Trouble erupted in the region last week after an attack on a convoy of northern soldiers and UN peacekeepers was blamed on southern Sudanese forces. Northern officials moved tanks into Abyei's main town and have since ignored pleas from the United States and United Nations to withdraw, saying the land belongs to the north.
South Sudan's President Salva Kiir said yesterday that the northern troops presence wouldn’t start a war or stop the south becoming independent from the north in July.
"There's real concern that the government of Sudan may have taken a decision to continue to occupy Abyei for its own political advantage for an indefinite period," US ambassador to the UN Susan Rice told Associated Press.