One of the four terminals at London's Heathrow Airport has been closed and evacuated while emergency services respond to an incident, the airport said.

LONDON: One of the four terminals at London's Heathrow Airport that was evacuated earlier on Monday (Sep 8) over what authorities called a "possible hazardous materials incident" has now reopen

Twenty people were assessed after reporting injuries but "no trace of any adverse substance was found", police said.

Heathrow's Terminal 4's check-in area was "closed and evacuated" Monday evening as emergency services responded to an "incident", the airport's operator said on social media.

In a post on X, the airport advised passengers not to travel to Terminal 4 as emergency services responded to an incident on Monday evening.

Heathrow Airport has said Terminal 4 is safe to reopen after it had been evacuated earlier today while firefighters responded to a "possible hazardous materials incident".

A 'possible hazardous materials incident' saw Terminal 4 shut for around three hours shortly after 5pm on Monday, forcing crowds of people to gather outside while emergency crews rushed to the scene.

The Metropolitan Police said “no trace of any adverse substance” was found.

Heathrow Airport Terminal 4 has closed and passengers have been urged not to travel there as emergency services arrive in response to a "possible hazardous materials incident"