JOSO, Japan — Raging floodwaters broke through an embankment Thursday and swamped a city near Tokyo, washing away houses, forcing dozens of people to rooftops to await helicopter rescues and leaving one man clinging for his life to a utility pole.

There were no immediate reports of casualties, but rescue officials said they were overwhelmed by pleas for help. More than 30,000 people fled their homes, and hundreds more were stranded by the water.

As heavy rain pummeled Japan for a second straight day, the Kinugawa River broke through a flood berm, sending water gushing into the eastern half of Joso, a city of 60,000 people about 50 kilometers (30 miles) northeast of Tokyo.

Aerial videos showed a wide swath of cityscape underwater, more than one story deep in some places. The rains came on the heels of Tropical Storm Etau, which caused flooding and landslides elsewhere Wednesday as it crossed central Japan.

Japanese broadcasters showed live video of rescuers being lowered from helicopters and clambering onto second-floor balconies to reach stranded residents.

In one dramatic scene, a rescuer descended four times from a military helicopter over 20 minutes to lift up four people one by one as a deluge of water swept around their home.