A flower adorned memorial arch was erected amongst the charred soil at the crash site. [Photo: Mirror]

Grieving relatives of the 157 victims killed in the Ethiopian Airlines plane crash have been offered bags of scorched earth to bury instead of their loved ones.

Identifying those killed in last Sunday's Boeing 737 Max crash will take so long that officials have begun delivering 1kg sacks of burnt earth to each of the victims' families.

Earth from the plane crash site was being made available for a planned memorial service in Addis Ababa on Sunday, according to Reuters.

Families have been told it could take up to six months to identify the remains of their loved ones.

An Ethiopian government official also confirmed the deliveries of soil.

“The soil came as it became impossible to identify bodies and hand over remains to family members,” one family member said.

“We will not rest until we are given the real body or body parts of our loved ones.”

Countries across the world grounded the 737 Max 8 and 9 aircraft after flight 302 crashed on March 10.

Flowers are seen as rescuers collect victims' belongings at the plane crash site. [Photo: Mirror]

The pilot of the doomed Ethiopian Airlines flight made a frantic call before it crashed killing all 157 people on board, it has since emerged.

Captain Yared Getachew 'sounded scared' and started to return back to the airport after reporting a problem, a source said.

Ethiopia's transport minister said on Saturday it may take "considerable time" for investigators to find the cause of the crash involving the new aeroplane.

"An investigation of such magnitude requires a careful analysis and considerable time to come up with something concrete," Dagmawit Moges told a press conference.

Relatives of the passengers killed in the incident are being encouraged to provide DNA samples either in Addis Ababa or at any overseas offices of Ethiopian Airlines.

Death certificates are expected to be issued in two weeks.

Passengers from more than 30 countries were on board the Ethiopian Airlines flight from Addis Ababa to Nairobi.

The Ethiopian investigation into the crash is being assisted by teams from around the world, including the US and France.

The aircraft's flight data recorder (FDR) and cockpit voice recorder (CVR), or black boxes as they are often called, have been recovered and investigators are hoping they will shed light on the tragedy.