The jihadists launched the offensive after suffering a series of setbacks at the hands of regime troops in recent weeks including the loss of the ancient city of Palmyra, which officials said residents would start returning to on Saturday.
The fresh fighting came ahead of a new round of peace talks due next week in Geneva following a ceasefire between the regime and non-jihadist rebels that has allowed Syrian forces to focus on fighting IS.
Residents said IS attacked the cement factory outside the town on Monday and that about 250 employees had gone missing.
"We haven't been able to reach our family members since noon on Monday after an attack by Daesh on the factory," said one resident of Dmeir, using an Arabic acronym for IS.
"We have no information about where they are."
An administrator at the plant confirmed that 250 employees had been unreachable since Monday.
The Syrian Observatory for Human Rights, a Britain-based monitor, said the fighting was heavy but the jihadists had not managed to gain significant ground.
"The most violent clashes are near the airport and the power plant, but IS has not entered either yet," Observatory director Rami Abdel Rahman said.
IS had seized five regime positions in the area, including two checkpoints, since Monday, he said, adding that 20 members of regime forces and 35 IS fighters had been killed in the clashes.
"We're in the eastern neighbourhood. The situation is very tense here," she said, asking not to be named out of fear for her safety.
"We have no electricity, we have no water. There are people fleeing from the eastern districts to the west," she said.
Last month's fierce street battles in Palmyra left much of the city's residential neighbourhoods severely damaged.
Most of Palmyra's pre-war population of 70,000 people fled west towards the city of Homs when the extremist group advanced on the city in May 2015.
