"It's risky to operate large machines under such conditions," said Zhang Yefu, an engineer leading a team building makeshift shelters in Lushan county, Xinhua reported.
Moderate rain will remain in the region for the next few days, the National Meteorological Center has forecast.
Armed police have set up 20 rain-resistant tents in the Baosheng Township village of Yuxi and helped hundreds of residents move into the structures from tents they built after the quake destroyed their homes.
Rescuers in areas surrounding Lushan and the mountainous Baoxing counties fought major odds including falling rocks and landslides after rains Sunday to reach affected people in the remote areas of Baoxing, some of them having to walk long distances to reach their destination.
Chinese health officials in earthquake-hit Sichuan province are already dealing with meager medical supplies to prevent outbreak of diseases among the victims.
Along with other shortages of essential items including drinking water, tents, supplies and makeshift toilets, the more than 1.5 million people in the southwest province, affected by last Saturday's deadly 7-magnitude earthquake, also were in need of much-needed antibiotics and other essential medicines to treat the injured, authorities said.
"We have been eating instant noodles and pickles. Each of us is assigned with only one bottle of drinking water each day," one officer told the official Xinhua News Agency.
The latest official death toll rose to at least 193 including that of one rescue volunteer killed by falling rocks, while another 25 were reported missing, and the number of injured rose to more than 12,000, as tens of thousands of rescuers and military personnel, hampered by aftershocks, broken roads, falling rocks and landslides, pressed on to find survivors under the hundreds of collapsed homes and buildings.
"We should avert major public health challenges, particularly major epidemics in the affected areas," provincial health chief Shen Ji told a news conference, China Daily reported. He said a system for reporting infectious diseases will soon be established to beef up epidemic surveillance
Officials said makeshift shelters, set up after the earthquake, would remain the main focus of efforts to prevent the spread of infectious diseases as living conditions there among the large number of people are poor.
"We'll first carry out risk assessments for the main factors, including safe and clean water and food surveillance, basic public health conditions, insects that might spread disease to humans, and waste disposal around the shelters," one official said.
Xinhua reported makeshift toilets were urgently needed in Lushan County, the quake's epicenter, because the usual toilets could no longer flush since running water hadn't been restored. The report said it wasn't advisable to use indoor toilets because homes have sustained quake damage.
Among health concerns is the H7N9, a rare bird flu virus that has continued to kill people across the country since early this month.
Emergency doctors in Lushan County also said residents urgently need antibiotics to treat alimentary and respiratory infections, China Daily reported.
"Victims have access to only instant noodles, bread and cold water, which has led to many cases of alimentary tract infections," a local pharmacist said. "Also, it's easy for them to catch cold, staying overnight in the tent in the rain. The cases we have discovered include cough and pneumonia."
As of 2 p.m. Monday, 2,283 aftershocks had been recorded, including four with magnitudes of up to 5.9, official data said.
Earlier, the Civil Affairs Ministry said the earthquake and the aftershocks had affected 69 counties in the province. About 400 buildings were damaged and eight collapsed in Chongqing municipality and around 900 buildings were damaged in Yunnan.
Rescuers Tuesday began concentrating more on relief work, while still racing against time to find survivors, Xinhua reported. No major rescue progress, however, was reported in the two counties as of 9:30 p.m. Monday.
The rescue teams include 19,000 soldiers and officers from China's military and armed police forces, Xinhua said. The head of military rescuers said the troops had rescued four people out of debris, treated 2,875 injured and transferred some 1,355 tons relief materials as of 12 a.m. Monday.
"It will not end as long as there is a ray of hope," the rescue and relief headquarters in Lushan said in a statement.
It was in the same Sichuan province that a far more powerful earthquake five years ago killed more than 69,000 people, left several thousands more missing, and caused billions of dollars in damage, official figures say.