About 20 people have been killed in an explosion which destroyed a Brazilian space rocket just days before its scheduled launch, military officials have said.
Alcantara hopes to become a major centre for satellite launches
A spokesman for the Alcantara base in the north-eastern state of Maranhao said no wounded had been found.
One of the rocket's four motors caught fire, triggering an explosion which caused the launchpad to collapse as technicians were carrying out final tests.
The explosion was so intense that the exact number of victims and their identities have been difficult to establish.
"We were forced to hold a roll call of technicians" in order to work out who was missing, Defence Minister Jose Viegas said.
The failure of the VLS-3 rocket, which had been due to put two satellites into orbit, marks Brazil's third unsuccessful space bid since 1997.
"We had just done two days of tests and everything went well - 100%. Everybody is devastated," said Air Force Colonel Romeo Brasileiro.
Brazilian President Luiz Inacio Lula da Silva paid homage to the victims and their families, his spokesman said, adding that the president had reaffirmed Brazil's determination to pursue the space programme.
The blast happened at 1330 (1630 GMT) on Friday and was heard dozens of kilometres away in the town of Sao Luis. Brazil's Globo television showed footage of a plume of smoke rising over the base.
The BBC's Jan Rocha says the accident is a major blow for Brazil's space programme - not least because of the loss of so many skilled technicians.
The 20-metre-high (60 foot) rocket reportedly cost $6.5m. The two satellites - which were also destroyed - had been due to collect weather data for research programmes.
Ground control had been hoping to start the launch sequence on Monday, with the exact date to be determined by atmospheric conditions and final checks.
The last two rockets, which took off in 1997 and 1999, were destroyed in the air shortly after lift-off because of technical problems.
Just as news of the explosion started emerging, the head of the Brazilian Space Agency was holding a news conference with his Ukrainian counterpart about a deal to launch Ukrainian rockets from Alcantara.
"This sad accident should not and will not influence relations between Brazil and Ukraine," said Valeriy Komarov, the head of the Ukrainian Space Agency.
Alcantara hopes to become a major international launch centre for commercial satellites.
The base is close to the Equator, allowing rockets to use less fuel to reach orbit than from other bases.