The fighting erupted despite a new truce agreement reached Saturday which calls for forces on both sides to cease fire and pull back from the frontline to create a buffer zone.
The airport, which was severely damaged in a fierce battle in May, was hit by heavy artillery and the rattle of automatic weapons fire could also be heard, the journalists said.
Donetsk is the largest insurgent-held city in the conflict zone in eastern Ukraine but the airport remains under the control of government forces despite numerous rebel assaults.