Can I visit Hong Kong if I have China L visa

Rima, if you just return to mainland to catch a flight and the layover is not exceeding 24 hours, you don't need another entry permit for mainland. As for Hong Kong, you can enter there for a stay not more than 14 days without the entry permit. So you can visit Hong Kong.

Thanks Fanny for the reply. But the issue is my flight is 4 days after I come back from HK.
What kind of entry permit I would require and how will I get that

Well, then you need to apply for a G type I think. It's the easiest one to get. You can apply through the Commissioner's Office of the Ministry of Foreign Affairs in HK. The return ticket and your passport should be used.