WARSAW--Activity in Poland's manufacturing sector expanded in July, reaching a four-month high driven by accelerating new orders and the fastest growth of export orders since early 2014, Markit Economics said Monday.

The survey of 300 industrial companies showed the manufacturing purchasing managers' index rose to 54.5 in July from 54.3 points in June.

A PMI figure below 50 indicates contraction, while above that level signals expansion.

Output prices increased for the first time since June 2012, Markit also said.

Write to Martin M. Sobczyk at martin.sobczyk@wsj.com