March imports came in at 38.95 million tonnes, or 9.17 million bpd, according to the General Customs Administration. That compared with 8.286 million bpd in February and far exceeded an earlier record of 8.57 million bpd in December.

"The 9.2 million bpd of crude imports is definitely a shocking number. That means China built close to 1.7 million bpd of crude inventory in March, way off the chart from any perspectives," said Harry Liu, an analyst with consultancy IHS Markit.

IHS, as a result, expected a sharp drop to close to 8 million bpd in coming months as refinery maintenance picks up, and as available storage tank space dwindled, said Liu.

China's crude oil imports for the first quarter grew 15 percent over the same period a year ago to 104.73 million tonnes, or about 8.49 million bpd.

The customs data also showed that China's March refined fuel imports were up 10.2 percent on year at 2.7 million tonnes, while exports for the month rose nearly a quarter on year at 4.67 million tonnes.