Two million children in areas of Pakistan devastated by summer floods are still missing school, the UN children’s agency said.

The deluge, which began in mid-June, damaged or destroyed nearly 27,000 school buildings, Unicef said, adding it will likely be weeks or months before flood waters completely subside.

In some places, rooftops of the school buildings are only just starting to emerge, it said.

The record-breaking floods — which experts say were worsened by climate change — killed 1,735 people and displaced 33 million across Pakistan, mostly in the hardest-hit provinces of Sindh and Baluchistan.

According to Pakistani officials, 647 children were among those killed by the flooding.

Unicef’s education chief, Robert Jenkins, visited some of the flood survivors on Thursday and later said it is unclear when the children still missing classes will be able to return to school.

“Almost overnight, millions of Pakistan’s children lost family members, homes, safety and their education under the most traumatic circumstances,” he said.

Unicef has set up more than 500 temporary learning centres in flood-hit districts and provided support and school supplies for teachers and flood victims.

Pakistan has also asked the international community to scale up aid for the country’s flood survivors, now threatened by the upcoming winter.

On Wednesday, China announced an additional £60.4 million in aid to Pakistan, bringing China’s flood assistance to Pakistan to £133.2 million. The announcement came during Pakistani Prime Minister Shahbaz Sharif’s visit to Beijing.

China has so far been the largest contributor in response to Pakistan floods, followed by Washington, which has given £86.2 million in aid since June. The World Bank has estimated that the floods caused £35.5 billion in damages.