Tennis star Serena Williams was seen on Sunday (Dec 13) speeding to the finish line of her 5km charity run - in a taxi.

The world No. 1 stopped at the 2km mark of her Serena Williams Live Ultimate Run, held at Miami Beach, and hopped into a cab, which took her to the finish line.

Her sister Venus, world No. 7, completed the run.

About 3,000 runners took part in the run to raise funds for the Serena Williams Fund, which has contributed to many causes.

Later, Serena, 34, said in a video on Facebook: "I didn't run the whole way this year, but next year I will."

She was likely plagued by earlier injuries. In October, she cut short her 2015 season to recover from multiple injuries.

The four-time Olympic gold medallist did not play in the Women's Tennis Association (WTA) Finals in Singapore and the China Open in Beijing.

Serena said last Sunday that she was ready to play tennis again, and that she was "really injured".

"I just had to get better - you know, be able to just walk without being in pain," she said.

Her coach Patrick Mouratoglou revealed in November that she was suffering from knee injuries.