Trademark rights are territorial, and China’s system awards rights largely on the basis of who filed first. For an importer manufacturing in China under an unregistered brand, that creates a specific and well-documented exposure: a third party registers the mark locally, and the registration can then be used to block goods bearing that name from leaving the country.
The remedy is procedural and slow. The prevention is cheap and fast: file in China, in the relevant goods classes, before production scales — and consider a Chinese-character version of the mark, because that is what the local market and the customs system will read.
US search and filing start at tmsearch.uspto.gov and uspto.gov. Our guide: Protecting your brand and IP when sourcing.