South Wales Police confirmed five males between the ages of 15 and 21 were detained in the early hours of Thursday and remain in custody.
It follows the arrest of four during the riot, including two 15-year-old boys from Ely and Llanrumney, a 16-year-old boy from Ely and a 15-year-old girl from Roath.
They were released pending further enquiries and remain on police bail.
Harvey Evans, 15, died alongside his best friend Kyrees Sullivan, 16, when the Sur-Ron bike they were riding crashed in the Ely area of the city just after 6pm on Monday.
Their deaths sparked several hours of violence and disorder after word spread on social media that a marked police van had been pursuing the pair minutes before the crash.
CCTV from the area has since confirmed police were following the teenagers despite South Wales Police and Crime Commissioner Alun Michael dismissing it the following day as “rumour”.
Police said they are continuing to investigate both the crash and the riot which followed.
The Independent Office for Police Conduct (IOPC) has launched an investigation into “any interaction” between the South Wales force and the teenagers prior to the crash.
“The disorder followed a fatal road traffic collision in Snowden Road, Ely, which tragically claimed the lives of best friends Kyrees Sullivan and Harvey Evans,” a South Wales Police statement released on Thursday said.
“Our thoughts are with their families and friends, and everyone affected by this terrible incident. The families continue to be supported by family liaison officers.
“In relation to the disorder, nine people have now been arrested. Five of the nine were arrested early this morning (Thursday, May 25).
“Four males aged 16, 17, 18 and 29 were arrested in the Ely area and one man aged 21 was arrested in Tremorfa. They all remain in custody on suspicion of riot.
“This follows four arrests on the night and day following the disorder of two 15-year-old boys from Ely and Llanrumney, a 15-year-old girl from Roath and a 16-year-old boy from Ely. They are all on police bail pending further enquiries.”
“During the incident several vehicles were set alight, property was damaged, police officers were injured, and people were scared in their own homes,” they added.
“More arrests are expected as we continue to identify those involved.”
South Wales Police said as part of its investigation into the riot it has so far recovered 180 pieces of body-worn footage from police officers at the scene, and said officers are going through hundreds of hours of public CCTV and videos posted on social media.
The force appealed for witnesses to come forward with information, mobile phone footage, CCTV or social media posts that might help enquiries.