The Standard Club said that the first vessel was in Qingdao when it underwent a Port State Control (PSC) inspection by the Chinese Maritime Safety Administration (MSA) and was found to be using fuel with a sulphur content of 0.6777% mm.
The second vessel was in Xiamen and found by the MSA to be using non-compliant fuel having been at a berth for six days after changing to compliant fuel.
However, it is likely that previous high sulphur fuel residue remained in the engine fuel system resulting in emissions over the China ECA limit.
The ship was ordered to take effective measures to purify the fuel system.
The P&I insurer said it was unclear whether the Chinese authorities would fine the vessels involved.
They can be fined no less than RMB10,000 ($1,445) up to a maximum of RMB100,000 under Chinese regulations.
The violations are the first reportedsince the 0.5% cap on sulphur for marine fuel came into force on 1 January, with the transition appearing to have been relatively smooth so far.
