I have heard that from 1st September China will have a new immigration law and it will not be possible any longer to get a Chinese Tourist Visa in Hong Kong for longer than 1 month.
Does anyone have precise info?
There is no such regulation.
Visa consultancies in Hong Kong do not list such a change in the list of changes that will take effect on 1st of September. There are changes regarding extensions in Shanghai that will be bound to a proof that you have enough money for each day you want to extend the visa, but this does not touch the initial visa duration.
There might be a misunderstanding for emergency visas that can now be issued by public security bureaus on the border. Those can be only 30 days. Normal visa issued by the standard authorities such as foreign consulates can be still 180 days.