Recent monsoon rain has affected the supply of green leafy vegetables from Malaysia and caused the price of some of them to jump.

In particular, the prices of choy sum and bok choy from Johor Baru and Cameron Highlands have shot up by 80 per cent, say wholesalers.

Mr Jerry Tan, vice-president of the Singapore Fruits and Vegetables Importers and Exporters Association, said heavy rain has affected the supply and quality of vegetables from across the Causeway.

Malaysia's annual monsoon season continues unabated and Johor is facing the brunt of it, with some areas struggling with flood waters up to 2.5m deep.

As of Tuesday afternoon, the number of people evacuated in Johor state had more than doubled to 9,348, from 3,934 on Sunday.

Over two-thirds of the state's victims are from Kluang, Segamat and Kota Tinggi, the three most severely hit areas.

Vendors said that wet markets are more likely than supermarkets to be affected by the rain as they rely on a single or limited pool of supplies.

Mr Wong Kok Fah, who runs a family business at Kok Fah Technology Farm near Choa Chu Kang, said price fluctuations due to bad weather happen every year, but this year's has been particularly bad.

He said prices of some vegetables from Malaysia started to double about two weeks ago.

Related Story Expect a wet, cool Christmas with temperatures in Singapore likely to dip to 23 deg C in later half of December

Related Story Using green data to fight climate change

Prices of vegetables from other countries, though, such as China and Indonesia, have been stable. This includes tomatoes from Thailand and cabbage from Indonesia.

Mr Tan pointed out that other market factors affect prices. "It also depends on what farmers want to grow. Some crops take a month to grow, others two to three months. When farmers don't make money, they may switch to other produce and this will have an impact on supply," he said.

He noted that the price of Malaysian iceberg lettuce has gone up 30 per cent, and wholesalers have started to import this from Taiwan as well.

A vendor in Bishan said that the heavy rain in Malaysia has affected the quality of vegetables he gets.

"You pay more for lousy vegetables. There is no choice," he said.

Civil servant Felicity Lim, 50, lamented the high prices.

"When I visited the market a few days ago, there were not many green vegetables available. The choy sum was yellow and more expensive. But I will still eat my vegetables."