Up to 50,000 people a day are expected to attend the festival which is taking place at Glasgow Green until Sunday, with performers including Liam Gallagher, Snow Patrol, Amy Macdonald and The Chemical Brothers.
Festival goers have been arrived at the site under overcast skies since gates opened at 11am on Friday, some wearing face masks and many draped in Saltire flags.
Courteeners, Sam Fender, Blossoms and Inhaler were among the bands performing on Friday.
To gain access to the site everyone who attends TRNSMT must provide proof of a negative NHS Covid-19 lateral flow test (LFT), which must be taken no more than 48 hours before they arrive.
Ticket holders will be refused entry without proof of a negative LFT, and those attending on multiple days must take a second test 48 hours after the first one.