RFE/RL's Kazakh Service correspondent in Almaty, Danabek Bimenov, reports that no one was injured in the incident early today, which officials said was caused by an engine malfunction.
The rocket was carrying a Japanese telecommunications satellite.
But Talghat Musabaev, the head of Kazakhstan's national aerospace agency, Kazkosmos, told RFE/RL's Kazakh Service that the rocket was also carrying more than 200 tons of a highly toxic rocket fuel -- called heptyl -- at the time of the crash.
Kazakhstan's Emergency Situations Ministry said the Proton-M rocket's debris dropped about 40 kilometers from the city of Zhezqazghan, in the central Karaganda region.
"At the moment the relevant units of the Emergency Ministry are examining the area [of the crash]," Prime Minister Karim Masimov told reporters in Astana. "Those who are guilty will be punished and the ecological damage to our country will be compensated for by those responsible. The situation is under government control."
Kazakhstan's official meteorological service, Kazgidromet, was quoted by ITAR-TASS as saying within hours of the crash that prevailing winds were blowing toxic vapors from the crash away from nearby communities.
But a spokeswoman for the ministry, Natalya Kim, told RFE/RL's Kazakh Service that the focus now is on determining the direction of the wind at the time of the crash. She also said a government commission headed by Emergency Situations Minister Viktor Khrapunov will assess the environmental damage caused by the crash.
"Viktor Khrapunov expressed concern, noting that the fall of the Proton rocket was not a lone occurrence," Kim said. "Just last June, a Dnepr rocket crashed in [Kazakhstan]. And, as chairman of the commission dealing with the aftermath of [this] rocket crash, [Khrapunov] underscored that the commission's plan of action will include a full investigation of the aftermath of the crash for local residents, the natural environment, and animals."
Meanwhile, a Kazakh presidential envoy to Baikonur, Adilbek Basekeev, said all Proton-M rocket launches from that facility have been suspended.
Reports say at least two more Proton rocket launches were scheduled from Baikonur later this year.
Two Proton rockets crashed at Baikonur in July and October 1999. Kazakhstan's decision at the time to suspend all operations at the space center caused political tension between Astana and Moscow.
The Baikonur Center is regarded as one of the world's leading space facilities and is leased and operated by the Russian state space agency, Roskosmos.
(with Interfax, ITAR-TASS, Reuters, AFP)