The outlook puts the U.S. bank among the more bullish forecasts for the world’s No. 2 economy.

"While the domestic policy outlook going into 2018 has been broadly tracking our expectations, the global growth outlook has turned more upbeat lately," economists led by Hong Kong-based Haibin Zhu wrote in a note.

The upgrade comes amid evidence of accelerating demand for Chinese exports. An official factory gauge showed new manufacturing export orders climbed to a six-month high of 51.9 in December from 50.8 the previous month.

Still, heightened trade tensions between the U.S. and China remain a worry.

"While an all-out trade war is unlikely, we think the risk of miscalculation by either side resulting in an escalatory and broadened trade dispute is significant," JPMorgan’s economists wrote.