Mass layoffs started in Goldman's London office last week, and it sounds like they're going to continue everywhere.

One source told us that Goldman Sachs plans to lay off up to 20% of its employees in investment banking and securities.

Another source says 20% seems high. However there's no question that the original number of layoffs (1,000 globally) that Goldman had planned has been revisited and revised by a lot.

Here's what we know about layoffs at Goldman so far.

During Goldman's 2Q earnings call, David Viniar confirmed that Goldman planned to layoff 1,000 employees globally to save $1.2 billion. That number had been revised to save $1.45 billion ahead of 3Q earnings, according to Dealbook. However that revision would only have brought layoffs up to about 1,200 globally. So it sounds like it's been revised higher since then. The securities division at Goldman is huge. It's home to the firm's trading operations, its position management and its client operations.

Goldman announces earnings tomorrow, so we should know more then. In addition to layoffs in London, layoffs also started last week in Goldman's San Francisco and New York offices.

The London office is subdued, understandably, according to our source.

The severance package is better than UBS employees got. At UBS, laid off employees we spoke to got 3 weeks of severance per the number of years worked at the firm. That is not the severance package at Goldman, at least not for some.

A spokesman for Goldman did not have a comment.