When to withhold. A U.S. company that pays U.S.-source fixed or determinable income (FDAP) — dividends, interest, royalties, rent — to a foreign person (the Chinese parent, a Chinese shareholder, a Hong Kong or BVI holding company) must withhold federal tax at the time of payment (IRC §1441 / §1442). Service fees follow the place of performance: work done by the parent's staff in China is foreign-source and not subject to withholding; work done in the U.S. is U.S.-source, exempt under the treaty where there is no permanent establishment, but only with the paperwork in place. Loan principal and reimbursed costs are not income.
How much. The statutory rate is 30%. The U.S.–China treaty lowers dividends (Article 9), interest (Article 10) and royalties (Article 11) to 10%; rent for industrial, commercial or scientific equipment is taxed on 70% of the gross amount, 7% effective. The reduced rate applies only if a signed W-8BEN-E is in hand before the payment: treaty article and rate claimed, limitation-on-benefits category certified, foreign taxpayer identification number provided (the Chinese unified social credit code works). Payments to a Hong Kong company cannot use the treaty — there is no U.S.–Hong Kong treaty, so the rate is 30%.
Who is liable. The paying U.S. company is the withholding agent and is personally liable for tax it should have withheld (IRC §1461): the IRS collects the tax, interest and penalties from the U.S. company, not from the Chinese parent. "Headquarters said no withholding was needed" is not a defense.
How to report. Withheld tax is deposited electronically through EFTPS: $2,000 or more undeposited at the end of a quarter-monthly period (the 7th, 15th, 22nd and last day of the month) must be deposited within three business days; $200 to $2,000 at month-end within 15 days after month-end; under $200 for the year may be paid with Form 1042. File Form 1042 (the annual summary) and Form 1042-S (one per payee and income type, to the IRS and to the payee) by March 15 of the following year; filers of 10 or more information returns in total must e-file. Form 7004 extends the 1042 filing date (not the payment); Form 8809 gives 30 more days for the 1042-S. Treaty-exempt payments withheld at 0% are still reported on Form 1042-S.