Nov 19 (Reuters) - The Baltic Exchange's main sea freight index, which tracks rates for ships ferrying dry bulk commodities, extended losses to a fourth straight session on Tuesday on tepid demand for capesize vessels.
* The Baltic index, which reflects rates for capesize, panamax and supramax vessels, fell 34 points, or 2.5%, to 1,304, its lowest since June 25.
* The capesize index dropped 60 points, or 2.3%, to 2,543 points.
* Average daily earnings for capesizes, which typically transport 170,000-180,000 tonne cargoes such as iron ore and coal, decreased by $816 to $19,814.
* China has started an investigation into the production capacity of its steel mills on increasing worries about the rapid output growth this year, a circular showed, putting mild pressure on Chinese iron ore futures earlier on Tuesday.
* The panamax index rose 4 points to 1,116 points, snapping a 25-session long losing streak -- its biggest in more than 9 months.
* Average daily earnings for panamaxes, which usually carry coal or grain cargoes of about 60,000 tonnes to 70,000 tonnes, increased by $38 to $8,962.
* The supramax index shed 7 points to 716. (Reporting by Nakul Iyer in Bengaluru)