There was no casualty in the mishap, they said.
Efforts were on to stop the gas leakage because of which foul smell was spreading in the area and some people also complained of eye irritation and nausea, Thane Municipal Corporation's RDMC cell chief Santosh Kadam said.
The liquid ammonia bulk carrier overturned and fell in a nullah near Mumbra toll plaza close to the bypass at around 2.45 AM, he said.
Those residing in the nearby area were shifted to safer places as a precautionary measure, Kadam added.