Donald Trump has lashed out at Elon Musk after the billionaire unveiled plans to launch a new US political party, calling him a “train wreck” in an escalation of the feud between the US president and his former ally.

More than a month after their initial social media bluster, Elon Musk has announced the formation of a new U.S. political party in response to U.S. President Donald Trump signing his sweeping tax and spending bill into law.