Patrons have been let back into Melbourne Zoo after it was earlier sent into lock-down when an orangutan managed to escape from its enclosure.

It's believed Malu the Sumatran orangutan used a blanket as leverage to break the top wire of his enclosure, before walking along the roof to briefly escape.

Melbourne Zoo Director Kevin Tanner said patrons were promptly sent into a lockdown area.

"They were completely safe ... at no time were staff or visitors at any danger at all," he said.

One patron told 9NEWS visitors were politely "shuffled into the bistro" and given drinks while waiting to be let back in.

The 11-year-old was captured after being distracted with treats, while a tranquilliser was administered to his shoulder by a zookeeper.

"He'll wake up tomorrow morning not knowing exactly what happened, but thought he had a good time," Mr Tanner said.

Malu escaped the orangutan enclosure. (9NEWS)

Witnesses reportedly saw Malu use a blanket to hoist himself out. (9NEWS)

Zoo vet staff are now working to assess the inquisitive orangutan.

Visitors to Melbourne Zoo were allowed out of lock-down shortly after 4.30pm

Zoo patrons were ushered into secure areas. (9NEWS)