Zulfiya Gabidullina set a new world record in the 100m freestyle swimming.
China has won most gold medals so far with seven, followed by the UK with five and Uzbekistan with three.
The Games had a rocky start, with Brazil's president booed at the opening ceremony and a Belarussian official banned for holding a Russian flag - Russia has not been allowed to compete.
However fears that budget cuts and low attendances could affect the event have been allayed following a cash injection from the federal government and a last-minute surge in ticket sales.
Gabidullina took nearly a second off the previous world record in the S3 class, for athletes with amputations, no use of their legs or severe coordination difficulties, finishing in 43.22 seconds. Previously a wheelchair racer, she only took up swimming in her 30s.
Host nation Brazil has won two golds, including Ricardo Costa's win in the long jump T11 class, for athletes with total blindness.
Costa jumped 6.52m on his last jump, beating Lex Gillette of the US who had jumped 6.44m and had to settle for his fourth straight Paralympic silver medal.
"I like R&B," Gillette told NBC. "I guess I'm going to be playing the blues for a little bit right now."
Costa follows in the footsteps of his sister Silvania Costa, who won gold in the T11 category at the World Championship in Doha in 2015 and is due to compete in the Paralympics later.
The siblings suffered Stargadt disease, an inherited eye condition that affects part of the retina, Globo reports.
Uzbekistan, currently third in the country ranking, won the first of three golds when Khusniddin Norbekov, 29, smashed the discus world record in the F37 class, for athletes with impaired coordination.
Norbekov threw 59.75m, adding 3.94m on to the previous record set by China's Dong Xia in London in 2012.
World records have also been set in power lifting, where Vietnam's Van Cong Le lifted 183kg to win the up to 49kg category.
Meanwhile Britain's Sarah Storey became the country's most successful Paralympian by winning her 12th gold medal in cycling. She caught compatriot Crystal Lane, who took silver, after only 1,375m of the 3,000m individual pursuit final in the C5 class.
The 38-year-old was born without a functioning left hand and competed in track events for able-bodied athletes before winning two gold medals as a Paralympic swimmer in Barcelona in 1992 and subsequently switching to cycling in 2005.
The Games initially risked being overshadowed by Brazil's well-documented political and economic problems.
Brazil's new president, Michel Temer, was booed at Thursday's opening ceremony and the BBC's Wyre Davies in Rio says he is regarded by many as an illegitimate leader after last week's impeachment of the elected president, Dilma Rousseff.
Andrey Fomachkin, the Belarussian official who carried a Russian flag into the opening ceremony, was banned for violating the International Paralympic Committee's (IPC) ban on political gestures.
Russia - which borders Belarus - has been blocked from taking part over allegations of state-sponsored doping.
"A hero has appeared amongst us," said Russian foreign ministry spokeswoman Maria Zakharova, describing the ban on Russian participation as "disgraceful and inhumane", Russia's Interfax news agency reports.
A 50-year-old Kazakh woman has won her country's first-ever medal at the Paralympic Games in Rio de Janeiro.