Thousands of commuters were left stranded at morning rush hour when Beijing Subway Line 1, which services much of the city's central business district, broke down Thursday. 

Beijing Subway said the shutdown was caused by an unstable power supply affecting signals in stations on the line.

"The external voltage appeared unstable around 8:13 am, resulting in an increasing  interval between trains. The line resumed normal operations in half an hour, around 8:44," said Jia Peng, Beijing Subway spokesman.

The power loss had a knock-on effect on the capital's other subway lines, which carry millions of travelers a day. 

Huge crowds were crammed into stations. Thousands of travelers were stranded, especially at transfer stations, such as Jianguomen Station.

Many stations closed, and passengers were told to to take a bus or taxi.

"But there were too many stranded people for the buses and taxis to cope with. I walked for 40 minutes after leaving Sihuidong Station, hoping to take a taxi, but I was not so lucky, so I had to catch a bus," said Chen Xiaomin, who works near Hujialou, Chaoyang district.  

Many commuters were late for work.

"I should have been at work at 9:20 am, but I was an hour late. It was a terrible experience," Chen said.

Because of the delay, commuters were calling their offices and homes, and some were yelling and cursing, said another passenger, surnamed Tian.

Beijing's subway system has encountered frequent malfunctions in past months.

On June 25, trains could not arrive and depart Sihuidong Station due to a railroad switch accident, which also stranded many commuters, China National Radio reported.