The city recorded 744.8 millimetres of rain between Saturday and Wednesday morning, the Beijing Meteorological Bureau said on Wednesday.
The rain destroyed roads and knocked out power and even pipes carrying drinking water.
It flooded rivers surrounding the capital, leaving cars waterlogged, while lifting others onto bridges meant for pedestrians.
Wang Hong-chun, 41, was with other rescuers in a rubber boat when it flipped over in a rapidly flowing river. Four of her teammates survived.
At least 26 people remain missing from the rains.
Among the hardest hit areas is Zhuozhou, a small city in Hebei province that borders Beijing’s southwest.
On Tuesday night, police there issued a plea on social media for lights to assist with rescue work.
Rescue teams traversed the flooded city in rubber boats as they evacuated residents who were stuck in their homes without running water, gas or electricity since Tuesday afternoon.
“I didn’t think it would be that severe, I thought it was just a little bit of water and that it would recede,” said 54-year-old Wang Huiying.
She ended up spending the night on the third floor of her building as the water seeped into the first floor, which holds her steamed bread shop.
All the machinery is now underwater.
It’s unknown how many people are trapped in flood-stricken areas in the city and surrounding villages. Rescue teams from other provinces came to Zhuozhou to assist with evacuations.
“We have to grasp every second, every minute to save people,” said Zhong Hongjun, the head of a rescue team from coastal Jiangsu province.
Zhong said he had been working since 2am. Wednesday when they arrived, and expects to work into the night.
They’ve rescued about 200 people so far.
At least 21 dead as massive floods sweep Beijing
“A lot of the people we saved are elderly and children,” he said.
On Wednesday, waters in Gu’an county in Hebei, which borders Zhuozhou, reached as high as halfway up a pole where a surveillance camera was installed.
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Gu’an county resident Liu Jiwen, 58, was evacuated from his village on Tuesday night.
“There’s nothing we can do. It’s natural disaster,” he said.
Two other people were trying to pass through the flooded areas to rescue a relative trapped in a nearby village.
Nearly 850,000 people have been relocated, local authorities in Hebei province said.
The previous record for rainfall was in 1891, the Beijing Meteorological Bureau said Wednesday, when the city received 609 millimetres of rain.
The earliest precise measurements made by machines are from 1883.
Ma Jun, director of the Institute of Public and Environmental Affairs, called the recent rainfall “extreme.”
Last year’s total rainfall in Beijing did not even top 500 millimetres.
Ma said there should be a review of how cities are planned because some places experience repeat flooding.
“We need to avoid building large-scale construction … in low-lying areas,” Ma said.
The record rainfall from Doksuri, now downgraded to a tropical storm, may not be the last.
Typhoon Khanun, which lashed Japan on Wednesday, is expected to head toward China later this week.
The powerful storm, with surface winds of up to 180 km/h, may also hit Taiwan before it reaches China.
Thousands of people were evacuated to shelters in schools and other public buildings in suburban Beijing and in nearby cities.
The central government is disbursing more than $9.4 million for disaster relief in affected provinces.
The severity of the flooding took the Chinese capital by surprise.
Beijing usually has dry summers but had a stretch of record-breaking heat this year.