The case is the latest wrinkle in relations between Myanmar and China, which has continued to assert its growing economic clout in the Southeast Asian country even as some Chinese-led projects have sparked fierce local opposition.
Chinese foreign ministry spokeswoman Hua Chunying said a joint working group met each of the 155 detainees separately this week and "confirmed that they were in good physical and spiritual condition".
She did not provide any details regarding the date or circumstances of their detention.
Myanmar presidential office spokesman Zaw Htay confirmed Chinese nationals had been arrested in Kachin but did not specify how many.
"It's true that we have arrested some Chinese nationals. We will review them in line with immigration acts and forestry laws, then will take action," he told AFP.
Earlier this week China's state-run Global Times newspaper reported that "about 2,000 local residents, including hundreds of Chinese citizens" had been trapped amid fighting between Myanmar troops and the rebel Kachin Independence Army.
"According to information we get from the Myanmar side, we haven't found any Chinese people trapped in north Myanmar," she said, adding that Chinese authorities "hope that relevant media can respect facts and report objectively".
China has been ramping up its investment in neighbouring Myanmar, with the two signing a series of agreements in November worth $7.8 billion.
Yet relations have at time been roiled by intense local opposition to Chinese projects.
Last month a woman protesting a controversial Chinese-backed copper mine was shot dead by police.
The mine has triggered fierce opposition from local villagers due to alleged land grabs and environmental damage, with one recent protest near the Chinese consulate in Mandalay drawing around 500 people.