MUZAFFARABAD, Pakistan (AP) – Aid officials warned on Friday that almost all of the hundreds of thousands of tents distributed to quake survivors in Pakistan will not protect against the harsh Himalayan winter.

Pakistan’s army said it was constructing 5,000 shelters a day out of corrugated metal for the 3.5 million left homeless amid fears of a second wave of deaths as conditions worsen in the coming weeks.

An estimated 87,000 died in the Oct. 8 temblor, which caused devastation across a vast swath of Pakistan and India, mostly in Kashmir, the disputed Himalayan region divided between them. Winter started last month, and hundreds stream into hospitals every day for cold-related ailments such as pneumonia.

In Islamabad, Darren Boisvert, spokesman for the International Organization for Migration, said 420,000 tents have been distributed in Pakistan but “90 percent are not winterized.”

“Winterized tents are expensive, they are hard to procure, and must be shipped from overseas,” he said.

Boisvert said relief efforts have focused on the highest mountain villages, rather than the hundreds of thousands living in non-winterized tents in refugee camps lower down. He said 5,000 tents that are adequate for winter have been distributed to those above the snow line, and another 5,000 will be distributed by Dec. 12.

Jan Vandemoortele, the U.N.’s top aid coordinator in Pakistan, acknowledged a “colossal job” remains.

“The first snowfall last week gave us a taste of what the future will be,” he said at a news conference in Islamabad. “The situation remains very difficult.”

Vandemoortele said many villagers are choosing to stay put despite the hardships, and said no one will be forced to leave their homes. But he added that as the weather deteriorates, the number of people flowing into camps is expected to grow.

“We remain on a knife’s edge,” he said. “It may get worse before it gets better.”

Rain and snow have hampered aid operations, which still rely on helicopters to ferry supplies to communities in isolated mountains. Some roads have been closed and others declared unsafe.

On Thursday, a moderate aftershock was felt in northwestern Pakistan, Islamabad and some areas of Kashmir, according to Pakistan’s meteorological department.

Strong winds and colder-than-normal, subfreezing temperatures were forecast again for the weekend. The cold was expected to get particularly severe in the higher mountain villages.

The army said in a statement it has constructed about 30,000 shelters for quake survivors out of corrugated iron sheets, and is building 5,000 more each day.

Thousands in quake-affected areas have built additional shelters with the assistance of aid agencies, soldiers and volunteers.

Pakistan’s top relief official, Mohammed Farooq Khan, urged countries to send more winterized tents and corrugated iron sheets.

He said reconstruction activities would begin only after the completion of a survey to determine what areas are safe, probably in another few weeks.