The most recent happened at 7th and Howard streets just before 8:30 p.m.
Police say the driver ran a red light and killed the bicyclist.
This fatal hit & run in Golden Gate Park was the first of 2 deadly bicycle hit & runs tonight. Stories at 11p. pic.twitter.com/SH8N0bfFFR— Katie Marzullo (@KatieABC7) June 23, 2016
The driver took off on foot, but was arrested a short time later. Traffic was affected in the South of Market neighborhood because of the investigation.
Two hours earlier, a woman on a bicycle was hit and killed in Golden Gate Park just before 6:30 p.m. on JFK at 30th Avenue. The driver of the car took off after it happened.
Police were on the scene for hours investigating where the woman was hit and in the nearby area where the driver's car was abandoned.
Paramedics worked frantically to save the woman's life as she lay in the road in Golden Gate Park, her twisted bicycle lay nearby.
"I look and see the woman cyclist who had just passed us on the road fly up and I saw her bike fly the opposite way," said Timmory Johnson, a witness.
Police say the driver abandoned the car, a white Honda Fit with dealer plates, about a quarter mile away.
A witness says he saw two men in the car. He says they were going 50 or 60 miles an hour and passing other cars.
"They clearly went into the opposite direction traffic and went far enough over to run right into that lady head on," said Joseph Cucia, a witness.
Police continue to search for the driver and the passenger. The car was not reported stolen.