More than a quarter of a million people remain in need of urgent assistance almost a month after a large earthquake devastated the Papua New Guinea highlands.

The 7.5 magnitude quake hit on 26 February, followed by another two earthquakes and more than 100 aftershocks. It killed more than 145, displaced more than 34,000 and overall affected more than 544,000 people.

The PNG government estimates about 270,000 people, including more than 125,000 children, are in urgent need of assistance. About 143,000 are food insecure. Just 1,300 households have received emergency shelter.

Getting to the remote villages and communities remains difficult after landslides cut many off from road access.

“Children’s lives are in danger,” said Karen Allen, the Unicef representative for PNG.

“With limited access to basic necessities, families are struggling to survive in crowded shelters, or to rebuild homes and food gardens.”

Unicef estimated it needed at least $17m to provide humanitarian assistance over the next nine months. This week it delivered 23 metric tonnes of aid, including shelters, water purification tablets, hygiene kits, blankets and learning kits.

There are 24 organisations and companies providing relief or assistance, and US$48.7m in bilateral contributions have been provided.

Australia’s foreign minister, Julie Bishop, who visited the PNG capital of Port Moresby on Tuesday, announced a further assistance package of $3.4m, on top of the defence force aircraft and personnel already assisting, and a three-person medical team.

270,000 people are in need of immediate #Humanitarian assistance with food, shelter, water and health the key needs. Latest #PNG #earthquake humanitarian snapshot > https://t.co/kMJq02dERI pic.twitter.com/wNBoV5t35x — UN OCHA Asia Pacific (@OCHAAsiaPac) March 23, 2018

Noreen Chambers, a Unicef worker in the Highlands, said Unicef was concentrating on health, water and sanitation efforts.

“We’re also working in child protection, setting up safe spaces to provide psychosocial care to children and women and men affected by the earthquake,” she told Guardian Australia.

“We had about 400 children in one of our safe spaces in Mendi, taking part in games and reading to take their minds off the earthquake.”

Chambers said that as recently as last week there were at least 600 people living under one shelter at a Mendi emergency care centre – the only one Unicef was able to access by road.

“Now they have three tents set up, so there is some sort of help going in,” she said.

“The government is also working with other partners and they’re providing services to their centre.”

The crowded centres meant there was a risk of communicable disease outbreaks.

“If what I’ve seen at the care centre is the same in other places then you have a big number of people concentrated in one area with very limited safe water. At the place we went to the other water sources was a creek and it was really contaminated,” she said.

“As a result of that there were 20 cases of diarrhoea the week we were there. There was also a three-year-old girl who died.”

Damage in some of the four devastated provinces was so bad school may not re-open for the rest of the year, prompting warnings from aid workers that an entire generation of Papua New Guinean children risk missing out on a proper education.