LONDON (AP) — Part of a terminal at Heathrow Airport in London was evacuated Monday because of a possible hazardous material, authorities said.

The check-in area at Terminal 4 was closed and evacuated while emergency services responded, a Heathrow spokesperson said.

Crowds of passengers with luggage could be seen outside the terminal as firefighters responded to the scene.

The London Fire Brigade said the evacuation was a precaution.

The airport asked passengers not to travel to the terminal. All other terminals were operating.