As fast as possible or very quickly, referring to moving with great speed.

जितनी तेजी से कोई दौड़ सकता है

English Usage: He ran as fast as his legs could carry him to catch the last bus.

Hindi Usage: वह जितनी तेजी से संभव हो दौड़ा ताकि वह आखिरी बस पकड़ सके।