Slovakia, Latvia, Lithuania, Bulgaria, Romania and Malta, which had until now been considered second tier candidates, will join six other nations already in negotiation.
The EU opened talks with Poland, the Czech Republic, Hungary, Slovenia, Estonia and Cyprus in March 1998.
The Commission has also proposed giving candidate status to Turkey, although no negotiations will be started.
Ankara's human rights record has so far kept Turkey outside the enlargement process but improved relations with Greece - following co-operation over two recent earthquakes - have helped the Turkish cause.
Conditions apply
Commission President Roman Prodi said that for the first time since the fall of the Roman Empire there was an opportunity to unite Europe - not by force but on the basis of shared ideals and common rules.
It is believed the Commission's policy change on EU enlargement was prompted by the Kosovo crisis, which highlighted the strategic benefit of including the countries of Eastern Europe.
Wednesday's announcement will pave the way for EU leaders to abolish the distinction between first and second tier candidates, at a summit in Helsinki in December.
The Commission says Romania will not become a candidate until it improves its record on caring for orphans and speeds up its economic recovery.
Bulgaria will also have to show it has made economic progress and give a firm date for the closure of a nuclear power plant in Kozloduy.
Talks with the six new candidates should start next year. New members could be accepted as early as the year 2003.
Country profiles
EU aspirants seek negotiation deadline
(11 Oct 99 | Europe)
German Chancellor urges faster EU enlargement
(30 Sep 99 | Europe)
France supports Romanian EU membership
(28 Sep 99 | Europe)
Analysis: Shifting attitudes towards Turkey
(12 Sep 99 | Europe)
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