Up to 300,000 Rohingya Muslims could flee violence in northwestern Burmato neighbouring Bangladesh, a UN agency official has said, warning of a funding shortfall for emergency food supplies for the refugees.

According to estimates issued by United Nations workers in Bangladesh’s border region of Cox’s Bazar, arrivals since the latest bloodshed started 12 days ago have already reached 146,000.

Numbers are difficult to establish with any certainty due to the turmoil as Rohingya escape operations by Burma’s military.

However, the UN officials have raised their estimate of the total expected refugees from 120,000 to 300,000, said Dipayan Bhattacharyya, who is Bangladesh spokesman for the World Food Programme.

“They are coming in nutritionally deprived, they have been cut off from a normal flow of food for possibly more than a month,” he told Reuters. “They were definitely visibly hungry, traumatised.”

The surge of refugees, many sick or wounded, has strained the resources of aid agencies and communities which are already helping hundreds of thousands displaced by previous waves of violence in Burma. Many have no shelter, and aid agencies are racing to provide clean water, sanitation and food.

​Bhattacharyya said the refugees were now arriving by boat as well as crossing the land border at numerous points.

Another UN worker in the area cautioned that the estimates were not “hard science”, given the chaos and lack of access to the area on the Burma side where the military is still conducting its ‘clearance operation’. The source added that the 300,000 number was probably toward the worst-case scenario.

The latest violence began when Rohingya insurgents attacked dozens of police posts and an army base. The ensuing clashes and a military counter-offensive killed at least 400 people and triggered the exodus of villagers to Bangladesh.

In a letter to the UN Security Council on Tuesday, Secretary-General Antonio Guterres expressed concern that the violence could spiral into a “humanitarian catastrophe”.

Rohingya refugees – in pictures Show all 15 1 /15 Rohingya refugees – in pictures Rohingya refugees – in pictures A young girl and a baby wade through mud after arriving in Whaikhyang, Bangladesh from Burma on 10 September Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya refugees walk through a camp in Whaikhyang, Bangladesh after arriving from Burma Dan Kitwood/Getty Images Rohingya refugees – in pictures A young Rohingya refugee gathers firewood after arriving in Whaikhyang, Bangladesh from Burma Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya refugees wait for sacks of rice to be distributed in Whaikhyang, Bangladesh Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya Muslim refugees arrive on a boat in Whaikhyang, Bangladesh after crossing from Burma on 8 September Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya Muslim refugees react after being re-united with each other after arriving in Whaikhyang, Bangladesh on a boat from Burma Getty Rohingya refugees – in pictures Rohingya Muslim refugees walk along the remains of a road after arriving in Whaikhyang, Bangladesh on a boat from Burma Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya Muslim refugees wade through water after arriving in Whaikhyang, Bangladesh by boat from Burma Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya Muslim refugees wade through water after arriving in Whaikhyang, Bangladesh by boat from Myanmar Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya Muslim refugees stand in the rain after arriving in Whaikhyang, Bangladesh by boat from Burma Dan Kitwood/Getty Images Rohingya refugees – in pictures Indian children hold placards and shout slogans during a protest against the alleged persecution of the Rohingya Muslims in Burma EPA/Raminder Pal Singh Rohingya refugees – in pictures Supporters of the Difa-e-Pakistan Council (DPC), an Islamic organisation, listen to their leaders' speeches against Burma's persecution of Rohingya Muslims, during a demonstration in Karachi Reuters/Akhtar Soomro Rohingya refugees – in pictures Hundreds of Iranians take part in a protest against violence in Myanmar after weekly Friday prayers, in Tehran EPA/Abedin Taherkenareh Rohingya refugees – in pictures Indonesian Muslim activists hold placards and shout slogans during a protest against the alleged persecution of the Rohingya minority in Magelang, Central Java, Indonesia EPA/Ali Lutfi Rohingya refugees – in pictures Members of an Islamic organisation shout slogans against the Burma government during a protest in Dhaka, Bangladesh EPA

Based on the prediction that 300,000 could arrive, the WFP calculated that it would need $13.3 million in additional funding to provide high-energy biscuits and basic rice rations for four months.

Bhattacharyya called for donors to meet the shortfall urgently. “If they don’t come forward now, we may see that these people would be fighting for food among themselves, the crime rate would go up, violence against women and on children would go up,” he said.