Twitter user Helen True shared this photograph of emergency services attending London Bridge station where four people were taken ill.
Network Rail and TfL dismissed reports of a gas leak and said that overground and underground train services were running as normal.
More top news
Heavy downpours have triggered flash floods in Yorkshire.
The IMF's forecast for global growth has been cut to 3.1% - a fifth successive year of declining growth, the weakest performance since 2009.
Coronation Street actor Ryan Thomas is to quit the show after more than 15 years.