United Nations agencies say they do not have access to Palma in Mozambique's Cabo Delgado province.

Cabo Delgado was besieged by a group known as "al-Shabaab" terrorizing the area, and the UN agencies fear that people displaced by the conflict could reach one million by June.

UN Refugee Agency (UNHCR) spokesman Babar Baloch said on Tuesday that humanitarian groups are working non-stop to assist thousands of people seeking safety in northern Mozambique's Cabo Delgado province.

To make matters worse, those fleeing the violence by trying to reach neighbouring Tanzania are being turned back.

At a UN press conference in Geneva, Baloch spoke of "quite worrying reports for us" that more than 1,000 people tried to cross into Tanzania across the border from Mozambique.

He said reports the agency received has said that “more than 1000 tried to cross into Tanzania” from Mozambique.

“And they were turned back. At this stage, we don't know how this happened, who did this.”

The attack by the insurgent group known as al-Shabaab on the coastal town of Palma has forced out at least 11,000 people, with thousands more reported trapped inside the area.

"We have nearly 700,000 people who have been displaced all around the province itself," said Baloch.

"Our fears are if the violence and displacement continue like this, we could be crossing the one million mark by June. So, it's very important that civilians are protected."

He said the majority of new arrivals in Pemba, the province's capital, were women and children "with few belongings, most showing signs of severe trauma following the atrocities they witnessed and worried for those relatives who were left behind".

"The sudden and deadly nature of the attacks have left families torn apart, many still unable to leave. Among the vulnerable groups arriving in Pemba were unaccompanied children, separated families, and older people," said Baloch.

Tomson Phiri, UN World Food Programme (WFP) Geneva spokesman, said: "We are working with several UN agencies, and we are battling for access into Palma," despite reports of Mozambique government troops making it into the town.

"We are trying to pre-position food and assist people who have fled the attacks in Palma. Hunger continues to rise in Palma.

"Most people are unable to continue with activities. It is a coastal town. Some of them rely on fisheries, and they are unable to continue normal life as a result of the fighting and continued deterioration in the security condition."

Phiri said many people were struggling to survive, and that the people arriving in Pemba say they are struggling.

Insurgents who operate under the name Al Sunnah wa Jama'ah (ASWJ) and who are supported by ISIS militants in Iraq and Syria have consolidated their hold in Cabo Delgado and captured the city of Mocímboa da Praia last year.

"In terms of access, we are really struggling to gain access into Palma," said Phiri.

He said civilians have been arriving in Pemba, Nangade, Mueda, and Montepuez by foot, road, and boat since March 24 in the aftermath of the attacks.

"Humanitarian flights that helped evacuate hundreds initially have now been suspended pending further clearance by authorities," said the WFP spokesman.