BRUSSELS (REUTERS) - Toxic fumes from kitchen drains forced the European Union to switch the venue of an EU summit in Brussels less than 24 hours before leaders were due to begin a two-day meeting on Thursday (Oct 19), an EU official said.

The Europa Building, also known as "The Egg" and opened only in January amid controversy over its cost, was evacuated for the second time in under a week after catering staff were again taken ill due to fumes suspected to be leaking from the drains.

The summit will now take place next door, in the previous main venue, the Justus Lipsius Building.

About 20 kitchen staff were treated in hospital on Friday and an EU official said the Council and Belgian safety bodies were working on the assumption that Wednesday's incident came from the same source connected to the kitchens' drains.

It was unclear how many staff were made ill on Wednesday.

Highlights of the summit are likely include an address by British Prime Minister Theresa May to the other 27 on her Brexit plans over dinner on Thursday and a joint statement to be agreed by the 27 on Friday that will demand London offer tens of billions of euros more on its withdrawal in 2019 if it wants to start negotiating a future relationship based on a free trade pact.