A terminal at Heathrow Airport has been evacuated while emergency services respond to what has been described as a "possible hazardous materials incident". The Fire Brigade was first called to Terminal 4 just after 5pm. Heathrow Airport said the check-in area has been closed and advised passengers not to travel to the terminal. But all other terminals at the airport are said to be operating as normal. In a post on social media National Rail said trains are unable to call at Terminal 4. #Heathrow