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Electric car maker Tesla is vying with General Motors to become the most valuable auto company in the US.

On Monday, Tesla's market value passed Ford's after the firm's shares rose on news it had delivered a record number of cars in the first quarter of 2017.

Tesla's shares continued to rise on Tuesday, putting its value within a whisker of GM's $51bn market size.

Reuters reported earlier that Tesla had surpassed GM's value, but in fact at midday Tesla's value was $2bn lower.

Tesla's stock rose 7% Monday or was up another 1% on Tuesday - breaking through $300-a-share for the first time.

The share price rise was sparked by news that it delivered 25,000 electric vehicles in the first three months of 2017.

However, those sales were dwarfed by the 550,000 that GM sold during the same quarter.

Tesla has been at the forefront of battery-powered car technology and investors are banking on strong growth in the future.

In the summer, the California-based company, run by Elon Musk, who is also the chief executive of the rocket business SpaceX, begins production of its mass-market Model 3 sedan.

Tesla is also expanding its production of batteries for household and commercial buildings at a giant new $5bn factory currently under construction in Nevada.

In what was seen as a vote on confidence in the firm, last month China's Tencent spent $1.78bn on buying a 5% stake in Tesla.

After overtaking Ford's market value, Mr Musk dismissed criticism that the 14-year-old company was overvalued, tweeting: "Tesla is absurdly overvalued if based on the past, but that's irrelevant. A stock price represents risk-adjusted future cash flows."