They barged past security officials, displaying placards saying "Bowl out killer Mugabe" and "No cricket while Zimbabwe burns."
The group was led by British activist Peter Tatchell, who has twice tried to perform a citizen's arrest on Zimbabwe President Robert Mugabe.
"We are not going to sit idly by while people are starving," Tatchell said.
"They just barged straight through," an official said.
The England and Wales Cricket Board (ECB) is expected to announce at the conference whether they will play Zimbabwe.
Five days ago Culture, Sport and Media Secretary Tessa Jowell told the ECB that the government opposed the match because of security concerns and what she called the appalling human rights record of Mugabe's government.
Australia, Pakistan, India, Namibia and the Netherlands are also scheduled to play in Zimbabwe.
The World Cup, which will be staged in South Africa, Zimbabwe and Kenya, opens in Cape Town on February 8.
