US President Joe Biden was mocked online after he mumbled and bumbled during a speech on Tuesday.

A clip of the oldestever sitting president was posted to X by RNC Research, with users roasting Biden.

“Biden's brain malfunctions (again),” wrote X account RNC Research.

During Biden’s Tuesday speech, he announced the firstever federal extreme heat rule that protects workers.

The President’s announcement comes amid a scorching summer in the US, which scientists expect to be the hottest on record.

The new regulation will not be finalised until 2026 and is expected to cover roughly 35 million workers.