Less than half of the free umbrellas taken by commuters on rainy days as part of a Shanghai Metro project have been returned, according to the city's transport agency.

Passengers have been able to borrow the "Umbrellas for Love" since 2008, with all 280 stations initially issued with a stock of 100.

However, as the city is enduring daily deluges, staff at some stations say their stocks have run dry.

At South Huangpi Road Station on Monday, a sign stated that all umbrellas had been loaned out. A passing service center worker said: "Nobody gives them back."

An employee at Lujiabang Road station gave the same answer, saying they were waiting for a new batch to arrive.

"Due to public demand and the high rate at which the umbrellas disappear, we have had to distribute extra batches at least three times over the past few years," said Fan Wenjun, a media officer at Shanghai Metro operation management center.

Data provided by the center showed that of the 88,000 umbrellas allocated to stations, less than half are still in circulation. The return rate was 47.5 percent for the entire metro network in February.

Passengers can borrow an umbrella after writing down their name and phone number at the service center. Usually passengers will be reminded to return the umbrellas within a week to where they were borrowed. Each umbrella is numbered and belongs to a specific station.

A woman takes an umbrella at the Century Avenue metro station in Shanghai. The umbrellas are available to commuters free of charge on rainy days. [Dong Jun / for China Daily]