Brown, swirling water came up to Phoebe Wallis' neck as she struggled home through Beijing's deadly floodwaters which have killed at least 37 people.

The New Zealander walked barefoot through the floods on Saturday - the deluge washed away her sandals - to get home from the school where she teaches English.

"Seeing only heads in the water was very scary," the 23-year-old said. "And it was very difficult because the rain was so heavy."

The rain was the heaviest to hit China's capital in six decades. It killed at least 37 people and left cars and buses submerged.

Miss Wallis moved to the Haidian District in Beijing about two years ago.

The rain started about 11am on Saturday and kept getting heavier. By the time Miss Wallis left work, it was above her ankles.

Miss Wallis and a local Chinese left the school together and caught the bus. But when traffic came to a standstill, the pair started walking and she quickly lost her footwear in the muddy water.

"The floodwater was up to our necks ... . we could still walk but it was very hard walking through it," she said from Beijing.

"It was muddy water and you couldn't see anything. All the rubbish was floating. But it was quite tricky being in bare feet because I had to be careful not to step on rocks. And it was cold, very cold."

Miss Wallis talked to her mother, Kate, in Christchurch over Skype. Mrs Wallis was admittedly a "little worried" when told about the ordeal.

"I was just so incredibly thankful that she managed to get home - I was quite horrified," she said.

Chinese authorities worked through the night on Saturday to clean up the damage.

"Things happen very quickly around here," Miss Wallis said.

Local reports said 25 people drowned in the flooding, six died when their houses collapsed, one was killed by a lightning strike and five were electrocuted.

- Additional reporting AP