This is the dramatic moment two heroic boat crew members dived into a river to save a drowning pregnant woman in Thailand.

The Thai Smile Boat crew spotted the woman flailing in the Chao Phraya River after allegedly falling from a bridge in Nonthaburi, at the edge of Bangkok, on Thursday.

Footage shows Charkrit Sakharichanon and Suphak Phusuea grabbing life buoys before plunging into the muddy water. They fought the current to reach the struggling local.

The woman, who was five months pregnant, was hauled onto the vessel, where she was kept safe until police and rescuers arrived.

Police said the woman had reportedly fallen from the Phra Nang Klao Bridge, adding she was recovering at a hospital.