Alabir Sultanov bled to death almost immediately despite the best efforts of her father to fend off a dozen young men armed with baseball bats, metal chains and knives, police said on Tuesday.
Her father, Yusuf, and her 11-year-old cousin, Khursheda also sustained severe injuries during the unprovoked beating – perhaps caused by their Tajik appearance.
Racist attacks occur regularly in Saint Petersburg, Moscow and other large Russian cities - usually targeting Muslim students and migrants from the Central Asia and the Caucasus region.
Saint Petersburg governor Valentina Matviyenko demanded police should find the culprits "wherever they may be," adding that the crime was "as serious as the bomb attack in the Moscow subway" last Friday which killed 40 people.
The Russian presidential envoy to the northwest region, Ilya Klebanov, condemned what he termed "cruelty reminiscent of the Middle Ages," after holding a closed-doors meeting with top law enforcement officials.
"Cruelty reminiscent of the Middle Ages"
Russian presidential envoy
In Tajikistan, officials have expressed alarm at the murder and urged that Russian police act swiftly to arrest the assailants.
"This incident has provoked outrage and grave concern in Tajikistan at the attacks on our citizens in Russia by neo-Fascists and nationalist groups," said the Tajik foreign ministry's top spokesman - Igor Sattarov.
"The Tajik government expects the police in Saint Petersburg to take all necessary measures to find and punish the murderers," he said in Dushanbe.
An impoverished Central Asian state, over 15% of Tajikistan's 6.3 million population travel to other ex-Soviet republics, mainly Russia, in search of work each year.
Last year, Tajik authorities protested against the violent deaths of 600 nationals over the previous three years in Russia.