PERTH, June 27 (Reuters) – The recent plunge in freight rates has re-opened the price arbitrage for Colombian and South African coal to move into Asia, sparking renewed interest from Chinese buyers, trade sources said on Friday.

The Baltic Exchange's main sea freight index , which tracks rates to ship dry commodities, fell to its lowest in over eight months again on Thursday after posting its 21st consecutive sessions of decline.

Chartering rates for a capesize vessel from Colombia to southern China have fallen by some $10 earlier this year to between $25-$28 per tonne, while free-on-board prices for Colombian coal are in the mid-to-high $70 levels, which means traders are able to move Colombian material into China at a landed rate of about $105 a tonne, traders said.

For South African coal, FOB prices at Richards Bay port are hovering at $90 a tonne. Combined with freight rates of $16-$17, their landed price into China stands at about $107 a tonne.

''A price arbitrage has certainly opened thanks to the free-fall in freight rates and we're seeing fresh interests from Chinese buyers again,'' said a Singapore-based trader.

''But it's a very fickle market and the window can disappear very quickly, so sellers will have to be very quick and prompt to be able to do something.''

One trader said he sold a July-loading cape-sized shipment of Colombian coal into China two weeks ago at a landed rate of less than $110 a tonne, while another trader said he had just sold a July-loading South African cargo into China at about $107 a tonne this week.

The traders asked not to be identified due to commercial sensitivities.

Including the coal import tax of 17 percent, Chinese buyers are now able to buy Colombian or South African material as much as $3-$4 per tonne cheaper than domestic supplies.

However, industry sources said China's demand for coal imports have weakened considerably over the past few months, and that it was unlikely that there would a mad rush of orders for Colombian or South African coal that was seen earlier this year.