London: A beluga whale was spotted on Tuesday near barges in the River Thames near London, hundreds of kilometres from its normal Arctic habitat, witnesses said.

"Can't believe I'm writing this, no joke – BELUGA in the Thames off Coalhouse Fort," ecologist Dave Andrews wrote on Twitter.

Video footage showed the white mammal surfacing in the Thames near Gravesend, Kent, though no official identification has been made.

The RSPCA animal welfare group said it was "working with other agencies to monitor the situation". It said it was ready to provide help to the whale if asked to do so by other agencies.