In the 54-kg category, Jamuna stunned former world champion Ouidad Sfouh 5-0 in the pre-quarterfinal.
The 22-year-old, participating at the Worlds for the first time, dominated the bout as her punches were more accurate than the Algerian fifth seed on a consistent basis during the entire duration of the match.
The judges' points at the end stood 28-29, 27-30, 27-30, 27-30, 27-30 in Jamuna's favour.
Lovlina, on the other hand, defeated Morocco's Bel Ahbib Oumayma 5-0 in her last 16-clash in the 69-kg category.
Like Jamuna, Lovlina, who is last edition's bronze-winner, also dominated the three rounds and even though Bel Ahbib seemed to be having an edge in the final round, the Indian boxer came out with some timely and accurate blows to enter the quarterfinals.
The judges' points at the end stood 28-29, 27-30, 28-29, 27-30, 28-29 in Lovlina's favour.
Jamuna will now face Belarus' Yuliya Apanasovich, a bronze-medallist at the European Championships, who defeated Germany's Ursula Gottlob in her pre-quarterfinal bout.
Lovlina will be locking horns with sixth-seeded Karolina Koszewska, who defeated Uzbekistan's Shakhnoza Yunusova. A win there will ensure medals for India in the ongoing championships.
Apart from Jamuna and Lovlina, six-time champion and third seed Mary Kom (51 kg) and Manju Rani (48kg) are the Indian pugilist to reach the quarter-finals of their respective weight class.
Kavita Chahal will also be facing Kavaleva Katsiaryna in her last-eight clash in the +81-kg category. Kavita got direct entry into the quarters thanks to the small size of the draw in her weight category.
( With inputs from IANS )