Chinese AI chatbot DeepSeek sparks turmoil in US tech markets

Shares in major US technology firms have fallen steeply in value after the sudden emergence of a low-cost chatbot built by a Chinese artificial intelligence firm.

The DeepSeek app, which was launched last week and reportedly developed for a fraction of the cost of its rivals, has overtaken rivals including ChatGPT to become the most downloaded free app in the US.

Shortly after US markets opened, DeepSeek says it was hit with a "large-scale malicious attack".