STORY: China's BYD saw sales accelerate by just over a fifth in the second-quarter.

It helped the electric vehicle maker close the gap with rival Tesla for the title of world's top EV seller.

BYD sold slightly over 426,000 EVs in the April to June quarter, according to Reuters calculations.

That's around 12,000 fewer than Tesla's estimated deliveries.

The U.S. firm is expected to report a 6% drop in it quarterly deliveries on Tuesday (July 2).

If so, it would be the first time it's posted two straight quarters of decline.

Elon Musk's company is dealing with strong competition in China.

Demand has also slowed due to a lack of affordable new models.

The company may give up its top EV seller title to BYD if the actual results turn out to be softer than estimated.

Industry data suggests Tesla's China-made EV sales in June fell by almost a quarter from a year earlier.

Other Chinese EV upstarts like Nio also reported stellar growth last quarter.

By comparison, BYD maintained steady growth in EV sales.