Rao Xiping, head of the government's hydrometeorological station in Beichuan, one of the areas worst-hit by the earthquake, also said that the dam was safe for the immediate future but that water levels were continuing to climb.
However, Rao told Xinhua that the water flow through the sluice would need to more than double in order to satisfactorily drain the lake.
Lives under threat
Fears that the Tangjiashan lake would burst drove authorities to move more than 250,000 people as they hurried to build the diversion channel.
David Hawkins, Al Jazeera's correspondent in China, said that 1.3 million more people could be forced to leave the region in the coming months.
The potential collapse of the lake threatened to flood an area that is home to more than one million people and compound the misery in an area still reeling from the magnitude 7.9 quake on May 12 that killed at least 70,000 people.
Some people displaced by the earthquake have moved several times as the floods threatened those in refugee camps in central Sichuan province.
"I can't even cry, even if I want to. First, it was the earthquake, now it's floods," said Yu Taichun, a doctor who keeps watch over a small medical centre in a tent city of at least 2,500 people.
Yu said he has moved five times since the quake, arriving two weeks ago at the latest camp overlooking the town of Qinglian, about 30km downstream from Tanghiashan lake.
Zhen Yiyuan, 61, an evacuee camped in a hillside park, said his sister living in the destroyed mountain village of Yuli had it far worse, surviving only on salvaged corn and other crops after a few pounds of rice airdropped after the quake ran out.
The provincial government estimates that about 7,000 of the victims were children.
The national population and family planning commission has said it plans to send a medical team to the devastated area to help parents that have lost their only child.
China's family planning policies restrict most couples to one child, although rules allow for another baby if their child was killed, severely injured or disabled.
The medics will reverse sterilisation operations on couples that want to have another child.
"The team, comprised of experts of childbearing, will conduct surgery in the quake-hit areas to provide technological support for those wanting to give birth to another child," Zhang Shikun, a senior official with China's family planning commission, said.
Chinese authorities have also recorded 4,700 unclaimed children whose parents presumably died in the quake.
Zhang Shifeng, the civil affairs ministry official, said the final number of orphans was expected to be about 1,000 to 2,000, as children were gradually are being handed over to members of their extended families.