Screen images from Chinese social media appear to show the company warning customers that the SU7 Max delivery time could take up to 27 weeks.
Before the company started accepting sales on Thursday, it announced that within 24 hours, pre-orders had reached 88,898.
Xiaomi did not immediately respond to a request for comment from the news.
In the largest auto market globally, the technology behemoth is competing against EV rivals like Tesla and BYD. With a market share of roughly 12%, it is currently the third-largest smartphone vendor worldwide.
The pricing of the SU7 model is 215,900 yuan ($29,872; £23,663) for the base model and 299,900 yuan for the Max version.
The Tesla Model 3 has a starting price of 245,900 yuan in China.
The Tesla Model 3’s 567 km (or 700 km) is surpassed by the SU7, which has been compared to Porsche’s Taycan and Panamera models.
