Part of the $11 billion Metro rail tunnel project has been suspended after workers discovered a large exposed asbestos pipe while digging up St Kilda Road.

The asbestos pipe was unearthed last Friday, but project managers waited until this Thursday to stop work and begin to remove it.

They also waited until Thursday evening to put up signage warning the public of the find.

The exposed asbestos pipe is in the southbound lanes of St Kilda Road, opposite Melbourne Grammar School and the luxury Domain Apartments.

The road has been reduced to one lane in each direction but trams, cycling lanes and footpaths remain open.