According to the US-based SITE monitoring service, the claim was made in a brief Arabic message carried by the group's Amaq news agency. There was no immediate confirmation from Chinese or Pakistan officials.
Hours earlier the Pakistan army issued a statement saying its forces conducted an operation against the IS group earlier this month, killing up to 15 militants from Lashkar-e-Jhangvi Al-Almi (LeJA) who were in communication with IS about establishing a base in Balochistan.
Beijing is ramping up investment in its South Asian neighbour as part of a plan unveiled in 2015 that will link its far-western Xinjiang region to Gwadar port in Balochistan with a series of infrastructure, power and transport upgrades.
Pakistan has been battling Islamist and nationalist insurgencies in mineral-rich Balochistan since 2004, with hundreds of soldiers and militants killed in the fighting.
Bordering Iran and Afghanistan, it is the largest of Pakistan's four provinces, but the roughly seven million inhabitants have long complained they do not receive a fair share of its gas and mineral wealth.