The alarm was raised at 12.09pm at Charles Phillips & Sons, a well-known auction business based at Drummore House near Musselburgh.
Fire crews from Musselburgh, Newcraighall and Dalkeith were in attendance even after the blaze was extinguished around 4pm.
One eyewitness told the News: “The fire looks very bad - the smoke can be seen from Tranent town centre right into Musselburgh. It’s very heavy.”
Charles Phillips & Sons was founded in 1987 and specialises in the sale of art, diamonds, and memorabilia. The firm recently announced a company restructure.
A statement on its website said: “We are currently clearing all stocks and investments from our UK and overseas warehouse facilities. We will be using the expertise of Charlie Williams Auctioneer to sell our entire inventory.”
The blaze is the second serious incident Edinburgh fire crews have attended today. Earlier they were called to an incident at Greendykes House, Craigmillar, which saw one flat evacuated following a domestic fire.