The Fire Brigade have released a tweet suggesting the evacuation might be caused by a taxi on fire at the underground taxi rank.
P e r r y @Pezzlar Follow
Smoke bellowing from Euston Station. #evacuate #notgettinghome
London Fire Brigade @LondonFire Follow
We're also dealing with a taxi on fire on the rank outside Euston Station. One fire engine at the scene.
Read more: http://buzzfeed.com/sirajdatoo/londons-euston-station-evacuated-after-taxi-catches-fire