ANCHORAGE, Alaska (Reuters) - A four-time champion of Alaska's Iditarod Trail Sled Dog Race was first to reach the halfway point at a one-time gold mining settlement for which the wilderness trail is named, before quickly losing his nominal lead to another musher, race officials said on Thursday.

Lance Mackey, the only musher to win the 1,000-mile Iditarod four times in a row, drove his dog team on Wednesday night into the interior Alaska ghost town of Iditarod. His prize for being first to Iditarod is $3,000 in gold nuggets, officials said.

The race, which has grown from an obscure contest many considered a one-time lark into a world-famous, big-money sports extravaganza, began in Anchorage on Saturday and will finish in the Bering Sea town of Nome. Winners in recent years have reached Nome in about nine days.

In Iditarod, Mackey was joined by four other mushers - fellow four-time champions Jeff King and Martin Buser, and race veterans Sonny Lindner and Aaron Burmeister. All rested their teams at the checkpoint on Thursday afternoon.

But Buser later departed, snatching the lead from Mackey, who won the race in 2007 through 2010. Other teams could also overtake him as Mackey has yet to take a 24-hour rest that is required of all Iditarod competitors.

Buser has already taken that day-long mandatory layover, as have Burmeister and other top contenders who were on their way to Iditarod on Thursday, including 2012 runner-up Aliy Zirkle and 2004 winner Mitch Seavey.

There are no longer any people living in Iditarod, but every other year tents are erected and equipment flown in for a race checkpoint. The race route varies slightly by year, and in even-numbered years, the halfway point is Cripple, another abandoned mining settlement.

The Iditarod race commemorates a 1925 rescue mission that carried diphtheria serum to Nome by sled-dog relay. The Iditarod winner will receive $50,400 and a new truck. Other top finishers will also be awarded cash prizes from the race purse, which totals $600,000.

The name "Iditarod" derives from a local Athabascan term meaning "a far, distant place," according to race officials.