Extreme floods have hit China’s Three Gorges dam, which recorded the largest inflow of water in its history, prompting officials to assure the public it would not be breached.

Inflows to the world’s largest hydro-electric dam reached 75m litres of water a second, according to state media. By Thursday morning, 11 outlets of the dam had been opened to discharge 49.2m litres of water a second, the largest release since its construction.

After two months of heavy floods across central and south-west China, officials have promised the dam can withstand the flows.

A breach of the dam, a controversial and unprecedented feat of engineering along the Yangtze River, would be embarrassing for China, which took 12 years to build the megaproject, displacing millions and submerging swathes of land.

The Three Gorges dam, which can handle inflows of about 98.8m litres a second, is already approaching its capacity. Officials expect water levels in the reservoir, whose dam was built to withstand a water level of 175 metres, to reach 165.5 metres on Saturday. The flooding is predicted to last about five days.

This week the ministry of water resources said the standard of construction meant 111 large reservoirs upstream from the dam could help lessen pressure on the structure. “The standard of construction of the dam is high and it can resist large floods,” it said.

Upstream from the dam, officials in the city of Chongqing, in Sichuan province, evacuated almost 300,000 residents before the flooding. On Thursday, levels along the Yangtze near Chongqing reached heights not seen since 1981, when the country experienced its worst floods in a century, leaving 1.5 million homeless.

In Chongqing, roads, bridges, parks and a main highway in the commercial district were flooded, affecting 260,000 people and damaging at least 20,000 businesses, according to officials.

Images showed flooding had submerged three-metre-high signs and buildings several storeys high. Firefighters were using boats to transport trapped residents.

In Sichuan, emergency workers and volunteers were scrambling to protect a 1,200-year-old cultural relic, the Leshan Giant Buddha, as floodwaters reached the toes of the statue for the first time since 1949.

The provinces of Hunan, Henan and Hubei, where the Three Gorges dam is located, were also braced for heavy rain on Thursday.

The flooding threatens to derail the country’s fragile recovery from the Covid-19 crisis. The outbreak has caused an estimated 179bn yuan in losses and displaced more than 4 million people, according to officials.

The floods have also raised concerns about food security. A report from the Chinese Academy of Social Sciences said the supply gap was likely to be about 130m tons by the end of 2025.

The Chinese leader toured Anhui province this week, another badly hit area where floods had eased slightly. Xi Jinping stood atop a floodgate and visited soldiers, declaring: “I have always been concerned about the people in flood-stricken areas. The Chinese nation has fought natural disasters for thousands of years … We will continue to fight.”