F type extension and multiple entry

I will be staying in China for one month and applied for F type (multiple) as I will be leaving the country for one week and then coming back to stay for 5 days as a part of my research. But the Embassy only issue single entry on my visa. Due to lack of time, I could not apply for another one from my home country.

1. Is there any way to apply multiple F type in China ?
2. When is the best time to do it ? As soon as I reach China ?