Rescuers in south-western China are trying to stem the release of more toxic fumes from a burst natural gas well that killed at least 191 people.
The explosion sent gases shooting 30 metres high
But the operation to pump concrete into the well near Chongqing was put off for 24 hours, state media reported.
The decision was taken by a government team in the area to "aid the rescue effort," Xinhua news agency said.
Hundreds of people have been taken to hospitals suffering from poisoning and chemical burns after Tuesday's blast.
More than 40,000 people living within five kilometres (three miles) from the gas field have been evacuated, amid fears that the death toll would rise further.
Chinese President Hu Jintao has ordered the local authorities to do everything possible to speed up the search and rescue operation and prevent poisonous sulphurated hydrogen gas from spreading.
The BBC's Francis Markus in China says the accident is one of the most serious to hit China's natural gas industry.
Initial reports after the blast at the Chuandongbei field on Tuesday said only eight people had died.
But the death toll has been rising sharply, as people were dying in their sleep or on the roads fleeing the disaster area.
Reports of about 130 dead were followed in quick succession by news of 160 killed, then 190.
By Friday morning, 191 people were confirmed dead but rescuers were still combing the area, Xinhua said.
A nearby hospital was overwhelmed as it tried to deal with victims of the blast.
Local media showed pictures of children in a local hospital, their eyes sealed shut by the highly toxic gas, and of livestock littering the roads.
"The poisonous gas hovering in the air made an area of 25 sq km a death zone as many villagers were intoxicated by the fumes in their sleep," the China Daily newspaper said.
Operations were going normally before the gas suddenly exploded from the side of the drill, Qian Zhijia, deputy
head of the gas field, told Xinhua.
The accident sent a high concentration of natural gas and sulphurated hydrogen shooting 30 metres (100 feet) out of a burst well.
Rescuers were only able to ignite the gas spewing from the well on Wednesday in an attempt to burn it off.
The cause of the blast is still being investigated.
China is notorious for its dangerous working conditions.
An average of more than 10,000 people a month died in work-related accidents from January to September of this year.
China's natural gas industry is an emblem of modernisation in a country heavily dependent on coal, our correspondent says.
The field belongs to the China National Petroleum Corporation.
CNPC's subsidiary PetroChina began construction of a $400m gas pipeline from Chongqing to central China in August.