Adding the Mi 9 SE shipments, the total raises to over 1.5 million units (presumably this includes the Explorer version too). Note that the SE isn't available globally yet.
Last year, the Mi 8 series – not just the Mi 8 itself, but the Explorer and SE too – sold 1 million units in under three weeks. The trio went on to sell 6 million in four months. More recently, the Redmi Note 7 reached 1 million sales in a month. Note that these numbers are for sales, not shipments like the Mi 9.