More than 42,000 people displaced by the March 28 earthquake are living in temporary shelters that cannot withstand the expected monsoon next month, Save the Children warned.
More than 206,000 people were displaced by the 7.7-magnitude quake, around 42,000 of which are still in tents or other shelters that cannot withstand extreme weather.
They also lack access to clean water for drinking and washing, said the group.
The charity said ongoing aftershocks make people unwilling to return to their homes or start to repair damaged properties with the monsoon coming.
Early heavy rain flooded a camp for displaced families near Mandalay city.
Mandalay Region reported the highest earthquake death toll and destruction.
Jeremy Stoner of Save the Children said: “The nightmare is far from over for children in Myanmar. Many are living in temporary shelters that are inadequate in the long term.”
He added that communities were concerned about repairing important buildings before the monsoon.
“Donors must urgently respond with fast, flexible and muti-year funding that enables both immediate relief and early recovery,” said Stoner.
Save the Children said it distributed food and emergency household kits for more than 22,000 quake-affected people.
The World Health Organization warned of “rapidly rising health threats”, including tuberculosis, HIV and waterborne diseases, to tens of thousands of displaced people.
The UN’s health agency said quake-hit communities were living in overcrowded shelters without proper drainage or sanitation and facing an escalating risk of mosquito-borne diseases during the monsoon.
Up to 3,763 people were killed by the March 28 earthquake and the regime announced that at least 110 people remained missing.
The worst impacted areas were Mandalay, Sagaing, Magwe and Bago regions and southern Shan State and Naypyitaw, where more than 65,096 buildings were reportedly wrecked.
