Bond Air Services says it has temporarily grounded 38 EC135-model helicopters globally after discovering a "defect", Reuters reports.
More top news
Cloud and outbreaks of rain will ease away eastwards during the morning, clearing the east coast around midday with sunny spells developing.
Police and emergency services are attending the scene.
Rebel-held east remains at risk while the pumping station supplying the western part of the city is once again in operation.