Hi, I am from Hong Kong and is currently holding a B1 visa to work in the US for almost 6 months. My employer is intended to extend my stay to another 6 months. I will get salary pay from my HK employer for my stay in the US if less than 180 days. However, if I extend for another 6 months, will there be any tax liability here in the states? Can I leave US and return for a week or so?
Thank you,

If your total stay exceeds 183 days, all world-wide income earned while you are INSIDE the United States is subject to U.S. (and local and state) income taxes, irrespective of the income's source.

Leaving for a few weeks will NOT change that fact.