There were minor clashes between about 200 rival Sheffield United and Sheffield Wednesday fans as they made their way into Bramall Lane at about 7pm.
An eyewitness said bottles were thrown and a firework had been set off.
He told how trouble flared when Owls fans were being escorted by police along John Street towards the ground.
Meanwhile, The Cricketers' Arms - a favourite among Blades fans - was reportedly on lockdown with home supporters being told to stay inside.
The eyewitness said: "There were minor clashes and a few bottles thrown. There was a firework which went off aswell.
"It all happened very quickly but there were about 200 fans from both sides there.
"The police separated them and then they were just singing towards each other."
He added the mounted police division had also been called in to deal with the skirmishes.
Superintendent Simon Wanless, who is overseeing the derby day operation for South Yorkshire Police, tweeted: "Reports of fireworks in pubs in the city - don't spoil it!"
About 500 police officers, including some bobbies drafted in from other forces, are patrolling the streets tonight in a bid to keep a lid on disorder.