Witnesses said at least three of the victims died on Friday in a stampede as panicked fans tried to escape the fighting. More than 100 others have been injured in the violence.
State-run Syrian Radio reported the deaths as it began live coverage of the match, which was quickly called off. Police cordoned off the stadium and fired shots in the air to try to restore order.
Medical sources said four of the injured had bullet wounds, including an 11-year-old boy who had been shot in the stomach.
Witnesses said there were between 5000 and 7000 spectators at the match between Kameshli and Dir al-Zur.
Some of the 2000 visiting fans threw sticks and stones at the Kameshli supporters, they said.
"We had nothing to defend ourselves with because we were not expecting this, so we had to run and there was a stampede," a witness said.
Residents said the visiting fans were later evacuated from the stadium in army vehicles to avoid any further possible violence.
Elsewhere in Kameshli, there were sporadic reports of violence, and in one incident a policeman's house was reportedly torched. By late evening, the city was reported to be largely calm.