Snow, rain and strong wind, coupled with a drop in temperature, will descend on quake-hit Yushu county in the coming days, aggravating the misery endured by survivors and rescuers, a weather forecaster said on Sunday.

The temperature will fall by 4 to 6 C from Monday to Wednesday, chief weather forecaster Wei Shuxia, of the Qinghai Meteorological Bureau, told China Daily.

The temperature varies greatly by hours, she said. The mercury could be 15 C at noon, but fall below zero at night.

Wei said the lowest recorded temperature in Yushu in April once hit -12.8 C.

To make matters worse, the weather can vary within minutes. "It could be sunny one minute, followed by snow and then hailstones," she said, suggesting that the variation in weather, along with the altitude of 4,000 meters above sea level, hampers outsiders from adapting to Yushu's climate.

Altitude sickness and harsh weather were the biggest challenges to rescuers and quake victims, Li Wenzhong, who heads a rescue team from Xi'an, Shaanxi province, said in a phone call from Yushu.

"I woke up at night feeling cold," he said, referring to Saturday night.

Meanwhile, Qinghai has banned the use of advertising balloons to ensure the safety of flights that deliver aid to, and ferry victims from, Yushu county.

"We have suspended accepting applications to use hydrogen balloons, especially those for commercial use," said Yuan Zhaosen, director of the policy and regulation department of Qinghai Meteorological Bureau.

These advertising balloons, with a diameter of one or two meters, are usually tied with huge banners and fixed to the ground. They could pose a threat to flights if the balloons break free, Yuan said.

"In the worst cases, a flying balloon could cause a plane to crash," he said.

"Severe punishment" will be imposed on those who violate the ban, Yuan warned.

As of 11 pm on Saturday, a total of 226 planes have flown to and from Yushu, carrying 4,470 people and delivering 547 tons of aid, according to the Civil Aviation Administration of China.