A MiG-21 Lancer takes off during training exercises in Campia Turzii in Transylvania, Romania. File/Reuters

Eight military personnel died after their helicopter and fighter jet crashed on Wednesday in bad weather in eastern Romania near the Black Sea, marking the worst day of air force accidents in recent years.

The pilot of a Romanian military MiG 21 LanceR and the seven soldiers sent to find him on a search-and-rescue helicopter mission all died when their aircraft were involved in separate crashes late on Wednesday, the defence ministry said.

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The MiG was on an air patrol when it dropped off the radar in eastern Romania between the villages of Cogealac and Gura Dobrogei.

The EU member is on the front line to strengthen NATO's eastern flank as Russia is invading neighbouring Ukraine and has seen international reinforcements arrive in recent weeks.

The IAR 330-Puma helicopter crashed in the area of Gura Dobrogei, 11 kilometres (seven miles) from the airfield, the defence ministry said.

It was searching for the MiG 21 LanceR, shortly after the fighter jet — part of a formation of two MiG-21 LanceR planes performing air patrol missions -- lost contact and disappeared from the radar.

Later Wednesday, the fighter jet was also found, having crashed near Cogealac, an uninhabited area near the Black Sea, the defence ministry said.

The 31-year-old pilot died, it added.