Facebook Inc (FB.O), United Continental Holdings Inc (UAL.N), BMW AG (BMWG.DE) and others have spent weeks at Apple's headquarters, working with the smartwatch to test and fine-tune apps that will debut alongside the device, Bloomberg reported, citing people familiar with the process.
The watch, which will let consumers check their email, pay for goods at retail stores and monitor personal health information, will be Apple's first major product launch since the iPad in 2010.
The company has scheduled a special event in San Fransisco on March 9 where it is expected to showcase Apple Watch, which will be launched in April.
Apple uses extreme measures to keep its work secret - Internet access is blocked inside the rooms and no outside materials can be brought in, Bloomberg reported, citing a person who attended the tests.
Apple spokeswoman Trudy Muller and Facebook spokeswoman Johanna Peace declined to comment. Reuters could not immediately reach United Continental and BMW for comment outside regular business hours.
German carmaker BMW said on Thursday its talks with Apple did not involve developing or building a car, denying a German magazine report.