SIX students on an exchange trip to Bishop's Stortford have failed to board a return flight to Rwanda.
The students had been on an exchange programme from Rwanda and were taken to Hockerill Anglo-European College in Dunmow Road last Friday.
Two of the students, Antoinette Masoso, 22, and Delphine Ingabire, 20, left the rest of the group and failed to show up at Gatwick Airport on Saturday morning for their return flight.
The other four students went missing at Gatwick Airport during checking in.
PC Andy Gorrell, of Herts police's missing and vulnerable persons unit, said: "We are obviously becoming increasingly concerned for the welfare of both Antoinette and Delphine and would urge anyone who knows of their whereabouts to contact us immediately. We are working closely with police in Sussex to trace them."
Antoinette is black, around 5ft 9ins (1.75m) tall and of slim build. She has a short black hairstyle and was last seen wearing a navy hooded cardigan over a denim coloured blouse, dark blue jeans and dark brown leather flip flops.
She was carrying a light brown shoulder bag which had dark brown woven parts and a long handle.
Police say that it is possible that Antoinette had a change of clothes with her that may include a green track suit with an orange stripe down the leg and an orange logo on the jacket and T-shirt. She may also have a beige skirt with a sparkly decoration on the hem and a white sparkly blouse.
Delphine is black and about 5ft 4in (1.66m) tall. She was last seen wearing black jeans, a red shirt, a cream coat with a fur trimmed hood and a pink and grey small back pack.
Anyone with information should contact Herts police on 0845 3300222.