A genocide by the German empire against the Ovaherero and Nama communities in what is now Namibia killed tens of thousands of people from 1904 to 1908 and around 300 of the victims' skulls were sent to Germany for experimentation, 19 of which were returned by the government on Wednesday.

At a solemn ceremony at a church in Berlin, 19 skulls, a scalp and bones were given to a Namibian government delegation, but activists campaigning for recognition of and restitution for the Herero and Namaqua genocide said this was not enough.

"We demand a restitution ceremony in the German Bundestag which must be accompanied by the full acknowledgment of the genocide as well as an official apology by the German parliament and the Federal government," said the organizers of Apologize Now! Vigil for Victims of 1904-1908 Genocide, held outside the church.

In response to an uprising against colonial rule in German South West Africa, the empire began a campaign of extermination and collective punishment that lasted four years and is believed to have killed around 10,000 Namas and 24,000-100,000 Hereros.

After a brutal massacre in which men, women and children were slaughtered following a bloody battle, many Nama and Herero were herded into concentration camps where they were forced into slavery and a large number died of malnutrition and disease.

Their bodies were often used for experimentation and some 300 of their skulls were sent to Germany.

In 2011, German institutions began returning them, though some 250 are believed to still be there.