Just 20 percent of the 1.8 million single men and women who have registered at Shanghai's official matchmaking agencies have found the right person to tie the knot with.

Differences in income and education were some of the obstacles hampering the quest to find a suitable partner for life, the association overseeing the agencies said on Thursday.

Zhou Juemin, director of the city's matchmaking association, told the Shanghai Morning Post that the city is facing a "third wave" of singles, which started in 2007 and is forecast to last three to five years.

The biggest challenge is that these single men and women are difficult to match. The women will not compromise their expectations for an ideal husband, while most single men, who have been concentrating on their careers up to the age of 35 to 40, prefer women around 25, Zhou said.

Currently, the ratio of single men to single women is about 1 to 4 in Shanghai. Most of the singles are women aged from 30 to 35, according to the association.