More than 100GB of data was posted online on Wednesday.
The documents appear to show Twitch's top streamers each made millions of dollars from the Amazon-owned company in the past two years.
Twitch confirmed the breach and said it was "working with urgency" to understand the extent of it.
In a statement posted on Twitter, the company said it would "update the community as soon as additional information is available".
Fortnite streamer BBG Calc told BBC News: "The earnings list got my figure 100% correct."
Another streamer confirmed to the BBC that their earnings were "accurate" while a third person closely linked to a high profile player said the details were "about right".
Those behind the leak also claimed to have the source code for the video platform itself.
The documents, shared in online forums, appear to show payments made from August or September 2019 to October 2021.
Some versions shared online point to well known streamers, including Dungeons & Dragons channel CriticalRole, Canadian xQC and American Summit1g, as being among the top earners.
Twitch famously fiercely guards operational details such as how much its streamers are paid, so this looks extremely embarrassing for the company.
And it comes at a time when competitors such as YouTube Gaming are offering huge salaries to snap up gaming talent, so the fallout could be significant.
Aside from the salary details, the documents seems to contain the site's source code and even technical details for yet to be released products and platforms.
And evidence is building at least some of the data looks real.
Security experts tell me the files contains things such as internal server details that can be accessed by Twitch employees only.
And if it is all confirmed, it will be the biggest leak I have ever seen - an entire company's most valuable data cleaned out in one fell swoop.