Hopes of a baby panda being born in the UK this year are fading after the country's only bears failed to mate for a second day despite "natural sparks" flying between them.

The clock is ticking for Yang Guang and Tian Tian to mate within a limited window of fertility.

Keepers at Edinburgh Zoo opened a "love tunnel" between the bears' enclosures after tests showed female panda Tian Tian had ovulated.

They met five times yesterday, and "several times" again this afternoon, but despite "natural sparks" flying between them, the pair failed to do the deed.

The pandas will have a final chance to mate later tonight but keepers were losing hope that Tian Tian would get pregnant this year.

They said the attempted couplings had been "immeasurable" for the bears because they were both sexually inexperienced.

Each time the pair met we saw a huge amount of eagerness and attraction between Tian Tian and Yang Guang. There was lots of vocalisation and encouragement from our female and physical contact between the two. He mounted her several times, however full mating did not occur. Although both have bred before and have borne cubs with other pandas, they are both still relatively inexperienced. At the end of the day, this is year one of a ten-year conservation project here at Edinburgh Zoo. We are hugely encouraged by how much the natural sparks flew between the two animals, as like humans, not all male and female pandas are attracted to each other. Both were keen to mate but their inexperience showed.

Giant pandas Tian Tian (meaning Sweetie) and Yang Guang (Sunshine) arrived in Scotland from Ya'an reserve in Chengdu, China, on December 4 last year. They went on show to visitors for the first time on December 16.

An Edinburgh Zoo spokeswoman later said the pandas had met again twice on Wednesday evening and had come "closer than ever before" to mating, but again failed to do so.