A mountain river flooded by monsoon rains swept away the main bridge connecting Nepal with China on Tuesday, leaving 20 people missing, Nepali authorities said.

Rescue efforts were underway and an army helicopter was able to lift people stranded by the flooding. Police said dozens of rescuers were already at the area and more are expected to join in rescue efforts.

Security forces have rescued 55 people, including four Indians and a Chinese person so far, according to The Rasuwa District Administration Office. Nepal’s prime minister, Khadga Prasad Oli, along with top ministers and officials flew to the area.

The flooding on the Bhotekoshi River destroyed the Friendship Bridge at Rasuwagadi, which is 120 kilometers (75 miles) north of the capital, Kathmandu. Several houses and trucks that were parked at the border for customs inspections also were swept away. Hundreds of electric vehicles imported from China had been parked at the border point.

The 20 missing are 14 Nepali citizens and six Chinese nationals, said the National Disaster Risk Reduction and Management Authority. The Chinese and eight of the Nepalis were workers at a Chinese-assisted construction project on the Nepali side of the border, according to the Chinese Embassy in Nepal, quoted by state media.

The destruction of the bridge has halted all trade from China to Nepal through this route. The longer alternative is for goods to be shipped from China to India and then brought overland to Nepal. Monsoon rains that begin in June and end in September often cause severe flooding in Nepal, disrupting infrastructure and endangering lives.